I dunno. Though there are thieves in every group, I worry a lot less if the people shooting around me are serious players with their own stuff as opposed to renters out yahooing.
I'm not saying to throw all caution to the wind, but I don't worry about it nearly as much.
Had the same thing happen as another poster. Kept noticing a guy spying my XDM Competition that was on a table. Got nervous and went over. he was just curious about it. Nice guy. Let him shoot it and dang if he didn't shoot it better than I do.