Say you live in a high-crime area, and you carry around a decoy purse. (Your real purse is stuffed down your underwear or something). The decoy wallet has a few canceled cards and a fake but realistic-looking check made out to one Phineas T. Barnum. Sucker Crook swipes your wallet, tries to cash the check, and gets arrested. Would there be any legal complications for you, original funny money owner?
Also, could they make fake credit cards that alert the police if a theif tries to use them?
IANAL but I don’t know of anything that prohibits you from carrying false documents on your person if you have no intention of using them for fraudulent purposes.
When a credit card is reported stolen, and someone tries to use it, the merchant is generally given an authorization code that says, in essence, “Keep the card.” Many merchants don’t like to do this as it involves a confrontation with a customer and possibly a dangerous one. The merchant is not instructed to call police AFAIK. The bank/association doesn’t have the mechanisms in place to automatically alert police that a stolen card is being used and where it is being used. So adding a new mechanism (i.e., flagged card) with no infrastructure in place to support it probably isn’t going to happen.
In the case of the guy who was trying to blackmail David Letterman, he was given a phony check. I think Letterman’s lawyer described the check as “designed to bounce.” However, that was presumably done with the cooperation of the police and the bank.
In the Letterman case, Letterman had met personally with his blackmailer. The purpose of the check was not to identify the blackmailer, but to prove the motive was financial in nature and not simply journalistic exposition.