Pornography is featured throughout the GTA series.
Appearances in games
In Grand Theft Auto: Vice City, there is a pornographic film company (InterGlobal Studios) on Prawn Island, run by Steve Scott. Several missions involve working for Steve, including meeting porn star Candy Suxxx.
In every Pornographic Shop of GTA IV there is a small TV playing, it is only just a repetition of a girl going up and down, implying an act of sex, which in this case, porn.