From Wikipedia :
Parental Advisory (short for Parental Advisory: Explicit Content/Lyrics) is a warning label placed on audio recordings that contain explicit content, such as profanity, violence, or sexual content/references. It was introduced by the Recording Industry Association of America (RIAA) in 1990 and adopted by the British Phonographic Industry (BPI) in 2011. The label was first affixed on physical 331⁄3 rpm records, compact discs and cassette tapes, and it has been included on digital listings offered by online music stores. In PAL-region territories, some video games featuring licensed music were affixed with the label in the late 1990s and early 2000s.