At everything on the opposite side of the screen, typically. There is a recording light for Meta glasses, but not one for iPhones, for example: the "recording" indicators are all user-side there.
When I'm on public transport, people generally face their phones in such a way that they'd only be filming your feet or the floor... They don't hold them up at head height in such a way that other people would be recorded. Maybe it's just a cultural thing
It's the camera of their smartphone.
Not sure if it's ON though.