Someone may inevitably try cashing in the cheque.
Will some fee be charged, will I land in jail?
I'll make it clear that cheque is a piece of paper, and I will not even sign a cheque...
An unsigned check should not be a risk unless someone forges your signature -- which could be a hassle but is probably not a serious risk if the account is already closed. If you are worried, "sign" the check as Void, which explicitly marks it as invalid.
Personally, I would shred the leftover checks. The risk is minimal, but why force yourself to worry? If you must use checks for your art project, you can have fake checks printed up, eliminating the issue.
No fees will be charged and no jail for you. Why? Because the account is closed.
It is an art project, fine. But, if you fear the impossible, just to be on the safe side fill out every check with technical errors: date too old or invalid, value in pennies or in millions, invalid beneficiairy and the like. Even if stolen, no bank will accept a check with errors. The check will never bounce back because it will not be a valid check.
