Get the "pull" from a "party popper" and wrap it in a dollar bill. Record the serial number of the bill (some crypto here maybe). Make it impossible to open the closet without setting the "pull" off, ie no trapdoor.
Fairly good tamper-evidence, and the token is hard (and very illegal!) to forge. Also the dollar bill is still spendable, so the only cost of your accesses are the "pull"s. Depends on your threat model, of course. -- Peter Fairbrother
