<Li> Yellow: A yellow title card exists solely for trailers hosted on the internet, with the wording stipulating "The following preview has been approved only for age - appropriate internet users ." The MPAA defines "age - appropriate internet users" as visitors to sites either frequented mainly by adults or accessible only between 9: 00 p.m. and 4: 00 a.m. The yellow card is reserved for trailers previewing films rated PG - 13 or stronger . </Li> <Li> Red: A red title card indicates that the trailer is restricted and when it accompanies another feature, the wording states "The following restricted preview has been approved to accompany this feature only ." For trailers hosted on the internet, the wording is tweaked to "The following restricted preview has been approved for appropriate audiences ." The red title card is reserved for trailers previewing R and NC - 17 rated films . Trailers hosted on the internet carrying a red title card require viewers to pass an age verification test which entails users aged 17 and older to match their names, birthdays and ZIP Codes to public records on file . </Li> <P> Jack Valenti, who had become president of the Motion Picture Association of America in May 1966, deemed the Motion Picture Production Code--in place since 1930 and rigorously enforced since 1934--as out of date and bearing "the odious smell of censorship". Filmmakers were pushing at the boundaries of the Code, and Valenti cited examples such as Who's Afraid of Virginia Woolf?, which contained the expressions "screw" and "hump the hostess"; and Blowup, which was denied Code approval due to nudity, resulting in the MPAA member studio releasing it through a subsidiary . He revised the Code to include the "SMA" (Suggested for Mature Audiences) advisory as a stopgap measure . To accommodate "the irresistible force of creators determined to make' their films"', and to avoid "the possible intrusion of government into the movie arena", he developed a set of advisory ratings which could be applied after a film was completed . On November 1, 1968, the voluntary MPAA film rating system took effect, with three organizations serving as its monitoring and guiding groups: the MPAA, the National Association of Theater Owners (NATO), and the International Film Importers & Distributors of America (IFIDA). Only films that premiered in the U.S. after November 1, 1968 had to carry the ratings . Walter Reade was the only one of 75 top U.S. exhibitors who refused to use the ratings . Warner - 7 Arts' The Girl on a Motorcycle was the first film to receive the X rating and was distributed by their subsidiary, Claridge Pictures . Two other films were rated X by the time the MPAA published their first weekly bulletin listing ratings, Paramount's Sin With a Stranger and Universal's Birds in Peru . Both were to be released by subsidiaries . </P> <P> The ratings used from 1968 to 1970 were: </P>

When did the motion picture rating system start