Bingo.
I HAVE seen figures with night vision goggles watching the crowd at movie preview screenings (the type radio stations hand out passes for). I figured they were with the studios, not federal agents.
Also, there is hidden stamping in the film prints themselves (at least dating back to the first Tim Burton Batman) so the studios can ID which print/theater likely spawned the bootleg.
Don’t know though with the internally leaked digital transfers (the ones that say “AWARD SCREENING AUDIENCE ONLY” or some such disclaimer) and film being replaced by digital projection.