I think what he's looking for is what words to put on signs to post in an area, so that people will be informed that if they pass those signs, then they will be in a film.
I know folks use this all the time, but I really don't think it provides true legal protection. (I am not an attorney.) It would be much too easy for someone to simply not see the signs. Not only that, but blind people, illiterate people, and people from other countries who don't read English, would never even know what the signs said. Not to mention the issue of minors. These people, in my opinion, still have rights and I'm not sure which way the law would rule on protecting those rights.
No doubt lots of people will weigh in here and tell us all the 'facts' about this situation, but as with ALL legal matters, if the OP truly wants to be sure he/she is legally protected, then he or she needs to consult a qualified attorney. Anything else is a risk.