So what does "NOTICE OF SURVEILLANCE CAMERA IN USE" mean?

Well, it means there is a Surveillance camera in use and they are telling you so. Can't explain it more simply than that I'm afraid.

It means don't take your clothes off, don't steal anything, don't pick your nose or your butt, cause there is a camera watching every thing you are doing.

Exactly what it says, you may be being watched by a security camera. If you don't have a good reason to be there, go somewhere else.

it means just what it says , there are security cameras in the area recording to watch for thefts and other crimes so you are on camera , do not do anything you don't want others to see because you're not in a private location by yourself

It means there are security cameras being used and monitoring your actions in case you are a thief.

Really? How hard is that to figure out? SMH!

Depending on which country you are in there are regulations that require users of CCTV to warn people that it is in use. My company here in the UK has CCTV security cameras around the site and we are required by law to warn visitor that they are in use . The signs are required to give a contact phone number for anyone with any concerns.

This is the consumer electronics > cameras forum for people who wish to buy cameras or get help with using cameras or taking photographs. It's really the best place for posts about surveillance camera notices! Try google.