1. Graffiti is vandalism.
2. Vandals always exist.
3. Answer these questions;
Will I get caught?
Will the penalty be unacceptable?
Will it be enforced?
4. If you answered no to any, the offense will occur.

Solution; Emphasis on the capture of one; penalty to be removal of all and any damage, whether they did it or not, monetary restitution, minimum 30 days incarceration.
Make no exceptions for under age et al. Allow no judge to "interpret" the rules.
Once the enforcement is accurate and equally applied, the vandals will think twice!

tagging by gangs should be illegal but graffiti itself is a true art form and there should no doubt be a place where people can express theirselves openly with their art..just because they choose a wall instead of a canvas and choose spray paint over regular paint doesnt make it any less of an art