Funny this post comes up, after just this last weekend, while I was packing up my stuff at the local public range, I was tapped on the shoulder by a friend who's the owner of a local gunshop, who'd been assigned to an adjacent bench. He surprised me by asking about range rules, and told me he'd never used the range before. Among the various rules I explained to him is, that while a "cease fire" is in effect, no one is permitted to even touch anything on the shooting benches, not just guns, but anything. And, shooters are required to remain behind a painted line, at some distance from the benches. Moreover, during cease-fire, while shooters are downrange checking and setting targets and such, it is forbidden to handle even cased firearms, such as to take them off the line and out to your vehicle.
This rule is enforced under the hawkeyed supervision of numerous armed Range Officers, who brook no violations and do not suffer fools gladly. Firearms left on the benches are required to be displayed with actions locked open and empty. Apart from the obviously salutary safety benefits of this protocol, it has the ancillary benefit of discouraging pilfering stuff from the shooting benches while you're downrange and not able to attend to your stuff. This is not the case behind the safety line, and guns or gear left there would be subject to the chicanery described in the OP.
I'm informed by my friend and Past President of the range-operating organization that theft of shooters' gear has been
almost unheard of during the range's decades of operation. Nonetheless, I am always in Condition Yellow, when it comes to leaving guns and other valuable stuff unattended at ranges, and prefer to have a companion paying attention when I'm not...