I had one of mine stolen. It was a huge pain in the ass getting it replaced because I couldn't get a new one without a police report (and of course re-issuing fees). I had to do a lot of running around so some kid could get an extra ten points on a scavenger hunt or a decoration for his wall (or whatever somebody would need a moped plate for).
I usually just use cable ties to hold my plates on now --if somebody wants to steal my plate at least they won't bend the shit out of the bracket trying to pry it off. Cable ties don't rattle loose either.