How about some sort of ID tag that would be permanently welded to the back side of the sign? I'm sure it could be done in any number of ways without damaging the face of the sign. Your current method leaves a LOT to be desired.
When it comes to expensive signs, someone will always try to cheat someone else out of their hard earned money but the harder you make it, the less they'll try! A permanently welded tag on the back would leave permanent damage if someone tried to remove it--Just my 2 cents as I really hate those that try to cheat!
