Like many, I've taken my cars to may shows and normally don't have any issues. I do put small signs "Look but please don't touch" which I think help.
I was at a large Mopar show in Florida once, however, when I left to check out a few cars and came back to find a young man (in his 20's) actually sitting in the driver's seat EATING a damn hotdog! I (fairly calmly) went up and said "What are you doing? Please get out of my car!
He just shrugged his shoulders and walked off. I was absolutely dumbfounded.
VTMopar