How's being quite without moving the money stealing? If somebody owns that money, and does have a backup as well, taking it and hiding it somewhere in your place gives him the opportunity to figure out he lost the paper wallet, and that he must move the funds as soon as possible. If he doesn't own a backup, the money are donated to everyone-- in the same manner as if you burned a banknote.

The Police is the best bet? Come on guys, be more confident with yourselves. I'm sure I'd make a better try than the Police would on finding the owner. I wouldn't even trust handing over a private key in the police department.