Given the conduct of some staff, I assume it will also be acceptable for passengers to wear such cameras?
(I suspect not)
What needs fixing is the service. Those signs saying "mistreating our staff will not be tolerated" are basically saying "our service is so bad that you will feel like mistreating our staff so you restrain yourself" - how about fixing the service first. When was the last time you saw a sign like that in a fancy restaurant, say?
Saw one in my (very good) dental practice yesterday. I think it's probably pretty standard across many industries these days.