This is an interesting thread. Personally, I would no sooner pick up someone else's model without permission than I would fly to the moon. Even when permission would be or is forthcoming, I still rarely do so. Pretty fundamental courtesy .
On the other hand, the signs DO NOT TOUCH, or similar are perceived as unfriendly turn-offs to many of these on lookers who we would really like to embrace and/or serve (why otherwise would be displaying our models?). In this regard, I would think that a more inviting, but still cautionary notice can be posted to the order of, for instance:
"Exhibition Etiquette: In full respect for the model craftsman displaying models for your enjoyment, we ask that all visitors fully refrain from touching or handling ANY of the models on display, at any time".
Perhaps wordy, but the idea is to speak courteously and respectfully; and while unsaid, the big stick can still be there.
When all is said and done, however, there were still be some recalcitrants who "were born in a barn" (my Mother's words).
A simple way to reduce both the urge and need for anyone to handle models on exhibit is to raise the table heights significantly, such as they did in Naperville some years ago, and Cocoa Beach soon afterwards. I am simply amazed about how many outfits are still absolutely blind to the fact that a significant part of the audience that these meets should be attracting (those over 40-45) simply cannot SEE models displayed on the standard folding tables. Bifocals make it even worse.
Denny S. Anspach MD