GNU Collaborative International Dictionary of English

Found one definition

1.       
   ‖Graffiti (?), n. pl. [It., pl. of graffito scratched]
   1. Inscriptions, figure drawings, etc., found on the walls of ancient sepulchers or ruins, as in the Catacombs, or at Pompeii.
   
   [1913 Webster]
   
   
   2. any writings or drawings on a surface in a public place, placed there without authorization of the owner of the object on which it is written.  Such graffiti are usually unwelcome, and are considered as form of vandalism.
   
   [PJC]