1970's X Rating Screen by GrayLord791 on DeviantArt

Whatever Happened to the X Rating?

MPAA Rating Bumper Rated X Remake (1970-1971) by TheAnthonyCorp on DeviantArt

cinema history - Why would a movie that appears pornographic via it's rating (X) receive an Academy Award? - Movies & TV Stack Exchange

Movie Poster of the Week: Rated X at the Quad on Notebook

Hollywood's Battle Against the X Rating, 30 Years Later - The Ringer

File:X MPAA.png - Wikipedia

Watch Quentin Tarantino Fave The Street Fighter, The First Movie To Get an X -Rating for Violence (NSFW)

The Best X-Rated and NC-17-Rated Movies in History

The X Factor Hat Rating System

MOVIE 'SCARFACE' RECEIVES X RATING - The New York Times