MPAA X18 Rated Logo by JamesMoulton1988 on DeviantArt

X (MPAA), Rating System Wiki

X rating - Wikipedia

The Brief and Scandalous History of the X Rating

The Best X-Rated Movies in History

What makes a movie X rated? - Quora

MPAA Rating Bumper Rated X Remake (1968-1970) by TheAnthonyCorp on DeviantArt

RetroNewsNow on X: 🎬On September 26, 1990, the Motion Picture Association of America replaced the 'X' rating with NC-17 (No Children Under 17 Admitted) / X

Which is worse, rated R or MA? - Quora

X-Rated Movies: 28 Provocative Films That Challenged the MPAA – IndieWire

Every Major Movie That Got Slapped With An X Rating