The most common and most likely answer to this crossword clue is the 8 letter word GRAFFITO
G
R
A
F
F
I
T
O
More clues leading to the result GRAFFITO
- Tag game outside involved tariff
- Try collecting flyers suitable for Banksy work?
- German noble has tantrum over evidence of vandalism?
- Grand artist with loud following — one leading to work like Banksy’s?
- Latent in zealot, if far gone to the left, is a type of vandalism
- Writing on the wall for schoolboys if raised among corruption, earning nothing
- Drawing of frigate briefly scribbled
- Tennis star agreed with love message on a wall
Buddy explains!

The straight part
We know that "message on a wall" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case message on a wall = graffito.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GRAFFITO mean?
GRAFFITO noun- (archaeology and related fields) An informal inscription, as by a worker or vandal.
- A single instance of graffiti in the art/vandalism sense.