graffiti

Graffiti is painting and writing sprayed on walls in public. Cover the graffiti, graffiti artists, remove the graffiti.

It is treated as art by some and as criminal damage by everybody who has to clean it, and both are correct at once. Technically graffiti is the plural of graffito, though it takes a singular verb in ordinary use. Tagging is writing a name, and a piece is a larger work. Note that Roman graffiti survives at Pompeii in quantity, most of it about the same subjects as modern graffiti.