Legal Question in Intellectual Property in California

Re: How can television use MPAA's copyrighted symbols in their rating system?

First, MPAA has a trademark, not copyright, in the symbols. Copyright protection is for works of creativity, like the film itself.

Simple combinations of letters or letters and numbers are not, by themselves, eligible for registration as a trademark. MPAA's trademark in these combinations is probably made possible by the letter combinations being displayed in a font and a particular rectangular box that make them distinctive. Perhaps the little graphical device you see in movie ads next to the box is part of the features necessary to make it distinctive enough to trademark.

It should be obvious that no one can copyright or trademark the letter "G," for example, except that a highly stylized single letter could be trademarked if certain other requirements were met.

This is not to imply that I'm certain that TV can get away with using the same letters in, say, a circle instead of a rectangle. Probably, but there would be some risk of a suit based upon a "likelihood of confusion" theory. I'd guess the two industries have already reached a truce on this issue, or that it's been litigated and settled.