graffiti

Graffito is an Italian borrowing into English, and its plural in Italian is graffiti. It is acceptable, however, to use graffiti as a singular when the meaning is "inscriptions in general": Graffiti has marred the walls on this block for far too long, though Graffiti have marred the walls... is the more technically appropriate. Graffiti is also regularly used as a singular to mean "an inscription": It's just another gang-related graffiti, though graffito is the more technically correct term.