system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do movie scenes in famous places (like Times Square or Grand Central Station) work? Do they have permission forms for everyone in the area?
gpt
If you live near one of these locations, sometimes without warning you attempt your usual walk past the area and find that it's blocked off for filming.  Sometimes there's a PA (production assistant) standing there with a clipboard.  He/she will give you a lookover to check that you're a visual fit for the show, and then tell you that you have to detour around *unless* you sign a release and promise not to draw attention to yourself as you walk past. 

They only do that for people walking by in the midground, though.  Anyone coming anywhere near the actors will be paid extras. 

(Really experienced New Yorkers know that things like sidewalks are always fair game [unless they've paid a fortune to block off the entire street for the shoot, in which case it will be police blocking the road, not crew] and can't be obstructed whether you refuse to sign a waiver or not.  Look in the background of some Law & Order shows and you'll see a grizzled local plowing through on their way somewhere with a worried production person trailing behind.)