Unfortunately, you likely have no legal standing to pursue a claim of "forgery". In any event, your boss apparently became aware that the two people did not actually sign the document, so forgery is not really an issue as to what happened to you. It also sounds as if you were a member of a union for federal employees, and/or your agency had a grievance process in place, which resulted in you getting your job back and presumably any "back pay" for the time you may have been out of work, before returning. As such, and setting aside the unfortunate aggravation you experienced, there may be no monetary damages that you suffered, upon which to base a lawsuit. You are in a rock and a hard place because nothing said indicates an illegal discriminatory basis for your being "targeted". Is there a way for you to transfer to a different department, agency, etc. to get out from underneath your present situation - if so, give it some consideration.
Sign up to receive a 3-part series of useful information and advice about personal injury law.