I use 1/4-20 stainless bolts with a lock nut to keep mine on.

Ive never had a tag stolen, but last summer someone hit the rudee inlet boat ramp lot and took the hitch pins. I was lucky enough to see the problem( another truck and trailer, trailer and hitch disconnected with the boat still in the water), before I experienced it.

There are some real low life's that prowl boat ramps. And they wonder why I carry.