Via Politech and info-commons.org, a demand letter from the MPAA to the owner of a website named RATEDNC-17.COM, which appears to distribute ‘themes’ or ‘styles’ for Linux. The MPAA Rating System consists of certification marks. The criteria for MPAA’s NC-17 mark is:
. . . IN THE OPINION OF APPLICANT’S RATING OR APPEALS BOARDS, MOST AMERICAN PARENTS WILL CONSIDER THE MOTION PICTURE INAPPROPRIATE FOR VIEWING BY ANYONE UNDER THE AGE OF 18, BY REASON OF ITS DEPICTION OR TREATMENT OF VIOLENCE OR SEX OR ABERRATIONAL BEHAVIOR OR DRUG ABUSE, OR A COMBINATION OF THESE OR OTHER ELEMENTS.
In contrast, the criteria for the MPAA’s “Rated R” mark is:
. . . IN THE OPINION OF APPLICANT’S RATING BOARD, IS AN ADULT FILM IN SOME OF ITS ASPECTS AND TREATMENT SO FAR AS LANGUAGE, VIOLENCE, NUDITY AND SENSUALITY ARE CONCERNED, AND THAT BECAUSE OF SUCH ELEMENTS NO NOE UNDER THE AGE OF 17 SHOULD BE ADMITTED UNLESS ACCOMPANIED BY A PARENT OR GUARDIAN.
The International Trademark Metasearch (free registration required) suggests that MPAA has extended its rights to Europe., where the ratednc-17.com website is apparently maintained.
There appear to be no valid U.S. registrations for the term RATED X or X RATED.
The MPAA ratings database is here.
An article on how the NC-17 rating evolved out of the X rating is here.