Good point! Here's one area that Mexico can teach us a thing or two. When vehicles are registered in Mexico they get the two license plates AND a matching full size window decal that must be placed on the inside of the back window. The decal is destroyed if anyone tries to peel them away. Having that decal makes the stealing of license plates a worthless venture. If the decal in the window doesn't match the plates, it's immediately apparent. This is a smart, cost effective answer to the problem of stolen plates.
Sounds good, but if they can duplicate drivers licenses, passports, green cards and matricula cards, a sticker would present no problem.
I wouldn't much care for a huge sticker blocking my back window.