Plate stealing is also an old Mexican trick. The traffic police would unbolt your plate (car or bike) for so called illegal parking. Used to be very common in Border towns. You'd have to go to the Cop shop and pay the "fine" to get plate back.
They stopped this practice years ago, but I still make my plate HARD to get off the bike. Red Loc Tite, smooth head bolt, odd sizes ... and one side different than the other. Torx security (center pin) fasteners are good for this too.
My plate is cracked too. I mounted it on a tough but thin piece of plastic, then mounted all up to the Lic plate mount. Seems OK.