This means WAR!

Above is an example of what's known as a Wide Area Release.  When shooting in a public place, theater, or anywhere there will be a large group of people, you will need to use a wide area release.  These should be made into posters that are about three feet tall, posted at every entrance to the location, and you'll need to have the camera crew get shots of all the signs, showing where they are posted.

For more info on wide area releases, I contacted a friend who works as legal consult to reality productions, and she had this to say:

In public places they cover people passing by in the background.  If people are focused on or lingering in the background they need to be individually released.  For audiences, they generally cover everybody although we still try to individually clear people we focus on for long periods of time and definitely for anybody with whom we interact.  For employees, or others that don't have a choice to leave the area, they in general need to be released.