Ytdyklly

Yes you are in danger.

However, anything your manager does (like printing a new letter over the signature) is fraud, and quite the bad variety too.

As she was doing what she was doing in the capacity of your manager, this is now the problem of your school/company/district or whatever the organisation is where you work.

HR is not your friend but in this case they will (or at least should) be your ally. To be a bit safer you could make it sound like you are just asking a question ("(describe in detail what happened), hey what was this about?", that way you get both documentation and can stay on polite footing with HR. I'd reccommend dropping by the office after the email too (if that is not too weird for a teacher in your district/area) just to chat up.

Do this now, get this on paper, leave the kids to twiddle their thumbs if you must.

Ok, maybe not leave the kids (as per comment) but I'd suggest getting at least a short "hey I have a question I'm very worried about, I'll email once I have time, mind if I drop by in the afternoon?" out of the way. Sociopaths have a tendency to proactively discredit their victims so you need to be ahead of that.

Speak to HR immediately, you signed a blank piece of paper - make sure it stays blank

Normally advice around speaking to HR is "HR are not your friend". However, this is in the context of bringing up general workplace greivances - as HR's remit is to protect the company, not the employees.

In this case, you have a manager who plans to break the law - by forging a document with your signature. This would put your kindergarten in a serious legal problem, especially if that forged document was ever used to terminate your employment. This is exactly the kind of situation HR do not want to happen.

You need to explain to them exactly what has happened (in writing via email, and then in person), and that there is now a blank sheet of paper with your signature, you believe will be used to fraudulently create a signed warning letter.

Importantly, I'd recommend you only focus on the potential misuse of your signature on the blank letter. Anything else, such as personal issues with this manager - will not necessarily be in their interest to help you with (and the usual "HR doesn't love you" advice applies).

For your personal sake; it's worth adding that while it was an extremely stupid move to sign that paper - it is understandable, and abusive managers have managed to push each of us to lower our personal standards at one time or another (so don't worry about how it happened, just get it sorted). Legally, that paper has no value, and you need to remember that you haven't legally given somebody the right to write whatever they want - you have unfortunately just given them the opportunity to break the law.

Amplifying what the other answers already said: Talking to HR is NOT enough, you MUST file a written report.

Write exactly down what happened with as much detail (time, location, names, quotes) as you can recall. Stick to the facts, don't put any emotion or interpretation into it. Take this report to HR make a copy for yourself. Make HR sign your copy and confirm in writing that they have received the report. Insist that they attach this report to your personell file.

You may want to have this looked over by a lawyer, before you file it.

Make sure you are friendly and co-operative with HR, but also be assertive when they try to push you off or ignore you. I don't think they can legally refuse to accept the report and confirm it's reception (again, a lawyer would help here).

Unfortunately, your blank signature could be a ticking time bomb. HR may try to sweep it under the rug and then it pops up 1 year later as a signed confession to something nasty. At that time, there may be entirely different people in HR. This needs to be documented clearly and you need written proof of it, so you have something to defend yourself with if you need it.

Ideally you get the paper back, but this may not happen. It's possible that your manager will simply deny that this happened. Or she may say "I already threw it away" or "I can't find it at the moment". HR won't be able to do much about this. Hence, you need thorough protection in writing.

Okay, in matters like this.

HR IS YOUR NEW BEST FRIEND

This manager is dangerous, and likely committing some fraudulent action. I won't scold you about signing a blank anything as you already realize the implications.

Write down all the events leading up to this, detail the event itself, walk into HR with your account and ask to see any additions to your file since that date.

The danger is not just to you, but to anyone else that deals with this person. HR needs to be alerted to protect you and any other employees who engage with him/her. This is one of the reasons HR exists, and this is absolutely a matter for them.

RUN, don't walk to the HR department.

The prevailing advice seems to be to talk to HR about it and document it there.

Note that a lot of these same people (on different questions) would probably tell you to not go to HR.

If the trip to HR does not go to your benefit, I think that you should write out what happened sign it, and get it notarized. That is admissible in court if the words above your signature turn out to be something other than what you were told they would be - and maybe even if they were what you were told that they would be.

There may also be a police report that you can file - as the intent could be fraud and you felt that you were under duress and had to sign the report. I presume you're under duress or at least stress because you mention how bad an idea it was to do that.

There are some notes about going to HR about "potential misconduct" which is part of why I'm taking the time to write this as a separate answer.

You can not control what your manager does. You can not anticipate what your manager will do. Speculating as to what your manager conceivably might do is a good way to give them an actionable grievance that you've yourself recorded with HR and turn this into a back and forth over something other than what actually happened, which is what you don't want in a situation like this.

You do need to document this with HR

But to be clear, you need to document only what you did and why you did it:

Your manager requested you sign a blank sheet of paper. You signed a blank sheet of paper and gave it to your manager, per their request. [You can repeat what they told you about why they were making that request, but I would avoid getting embroiled in that: ideally keep this as cleanly focused on the basic hard facts as possible, so there's not room for argument later on about who said what.] You didn't think anything of it at the time, and you try to be a good employee who does what they are told [or whatever you'd like to say in that regard of following orders], but for clarification's sake you would now like documented that what you signed was a blank sheet of paper, and that is the only thing you are agreeing to having signed, because THAT is what you signed.

If a date or something else was requested on it, note that. If it is literally just your signature, note that.

Don't speculate on what your manager might or might not do with the blank paper you signed. Don't accuse your manager of intending to commit fraud. (if your manager DOES commit fraud, then address it as such: but the key here is do NOT accuse them of something that they haven't actually done yet)

Do create a paper trail. Email it, BCC a personal account, and request to schedule a discussion or at least a "quick chat" in person with someone regarding making sure it gets properly documented. When you go, make sure you print off a paper copy to take with you so you have a reference of what you sent that you can refer back to if things get stressful, and as a reminder to keep it simply focused on the basic facts of what you did and that it was at the manager's request.

Don't make a big deal out of it: just be calm yet firm about wanting it documented. If HR (ideally) wants to make a big deal out of it, that's on HR, let them be the ones to press the concern and don't interject it yourself. Keep your own focus on what you did and why, and your expressed concerns related to that specifically, not on what your manager might or might not do. Don't be the one who turns it into a big thing, because other than being an odd and inappropriate request, nothing has happened yet. Don't accuse your manager of anything at this point. If necessary or pressed, you can state that your concern is something very mundane and not specifically related to your manager, like "what if it gets lost and someone else finds it?" but my advice would be to simply keep things straightforward as a matter of just wanting it documented in your record since it was at your manager's request, but that you have no specific concerns and just want an official record of having done so per request.

If you do this and it turns into something where HR has you sit down across from your manager regarding this, don't try to engage. Don't be the one who asks the manager why they did that. Don't speculate. Just stick to the line that you just wanted what you did per request documented, and that all you did was sign a blank sheet of paper, which is all you agree to having signed, which hopefully everyone can agree is an odd thing to have signed (again, do not speculate about what someone else MIGHT do with such a piece of signed paper, focus only on what you did and that it was per a manager's request/order). Again, if pressed on why you are wanting it documented, stick to your immediate concern over it being strange to sign a blank piece of paper, not what might or might not be done with it.

I note the most downvoted answers are saying "write it down"... and the most upvoted are saying "to document it, speak verbally with HR". That's backwards.

Comey that conversation

"To Comey" is a new verb that means to write down your recollection of events as soon as you can, because you feel there may later be disagreement over what happened. This should be done contemporaneously, or ASAP after the event. For instance, Comey sat in his car right after the meeting and wrote it down on a notepad. This proved very useful later.

I advise doing more. First, write down your recollection of the meeting. Be truthful and create a recording of the facts that would be difficult to challenge. Second, have it notarized, because you are not James Comey. That proves it was contemporaneous, and you didn't modify your recollection to suit the later situation.

Third, I would write a courtesy letter capturing in short form your recall of events. Something like this

Thank you for speaking with me today about the Jan. 3 incident, and hearing my side of events. As I said, I feel this and this and this, and you pointed out this and this and this. I recall we found a middle ground of this and this and this.

We also agreed that you would write a modified warning letter to that general effect. For expediency, you asked me to sign a blank piece of paper on which that warning letter would be later placed, and I complied. I would like to have a copy of that letter when complete.

Again, thank you for taking the time to discuss the matter with me. Usual salutation, signature.

Nothing threatening in there, and they don't know about the notarized note. You wouldn't use that or even announce its existence except to your own lawyer if things go that far.

Then, go have that verbal conversation with HR.