I know about WGA and Library of Congress copyright registration, but someone told me that films also get MPAA numbers on the scripts? Is this true?
You don’t need to worry about this. Really. Ever. At all. I’ve made a couple of big studio movies, and I’ve never seen an MPAA number on anything. But since you’re curious, I’ll tell you a bit about the the magic numbers.
The MPAA is a trade organization made up of the seven major film studios: Fox, Warner Bros., Sony, MGM, Disney, Universal and Paramount. While these studios compete fiercely with each other, they work together through the MPAA on issues of common interest, such as preventing piracy, maintaining copyright, and establishing ratings. The MPAA — specifically its president, Jack Valenti — is the "face" of the film industry to Congress.
Way down on the list of MPAA responsibilities is the job of keeping track of its members’ movies, for all sorts of internal reasons. That’s when a movie is assigned a number, which is probably the same "MPAA number" your friend saw on a script.
It’s nothing a screenwriter ever needs to worry about, but now you know.