Be aware that going on a major mission totally drunk out of your head will result in some truly spectacular artwork and at least one night in the cells.
When explaining yourself to the Police its worth being as reasonable as possible. Graffiti writers are not real villains. I am always reminded of this by real villains who consider the idea of breaking in someplace, not stealing anything and then leaving behind a painting of your name in four foot high letters the most retarded thing they ever heard of.
Remember crime against property is not real crime. People look at an oil painting and admire the use of brushstrokes to convey meaning. People look at a graffiti painting and admire the use of a drainpipe to gain access