Unwanted art (8)
I believe the answer is:
graffiti
'unwanted art' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for graffiti that I've seen before include "Wall scrawls!" , "Defacements on public walls" , "Scrawls on walls - fair gift" , "Scribblings on the walls of buildings" , "Scribbled drawings in public places" .)