CPTED means "Crime Prevention Through Environmental Design". In other words, don't make things easy for crooks.
A classis CPTED strategy for reducing graffiti is to put plants in front of walls that are easy to vandalise. This road side noise wall is a classic example - the RTA has planted all along the side of it facing the houses, and although the wall stretches for several hundred metres, this spot here is the only one with graffiti on it. The creepers and bushes do a great job of discouraging vandals. (I've written to the RTA and suggested that they extend the trellising to cover this spot so that creepers will eventually cover it over).
The rest of the wall looks like this - green, pleasant and clean.
It's not so easy to use this strategy where there's not enough sunlight to encourage plant growth. When that happens, you end up with "art work" like this.