Spray-painted writing (8)
I believe the answer is:
graffiti
'spray-painted writing' 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 scribbles" , "Scribblings on the walls of buildings" , "Unauthorised public writings" , "Scribbled drawings in public places" , "Unauthorised public writing" .)