MPAA X18 Rated Logo by JamesMoulton1988 on DeviantArt

X rating - Wikipedia

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

The X-Rated Girl & Others Lot (Film Ventures International, 1979), Lot #51399

CLOCKWORK ORANGE' TO GET AN 'R' RATING - The New York Times

This Film Is Not Yet Rated (Movie 2006): MPAA Gets an 'F

The X Factor Hat Rating System

DREAMS ARE WHAT LE CINEMA IS FOR: LAST SUMMER 1969

All the X-Men Movies Ranked - IGN

Where to watch X and the horror movie's age rating

When Ryan Gosling's Intimate Scenes With Michelle Williams In Blue Valentine Sparked A Rating Battle Because The S*x Felt Real