Grand Theft Auto: Chinatown Wars has been tagged with a "Z" rating (adults only) for the Japanese market, reports Siliconera:
All of the Grand Theft Auto games have been rated CERO Z so this isn’t really a shocker. However, Chinatown Wars will be the first Nintendo DS game with the rating and the second CERO Z game on a Nintendo platform. Killer 7 from Capcom is the other CERO Z rated game on Nintendo hardware.
CERO is the Japanese equivalent of the ESRB.