I’m not sure if the stuff that appears on the creek banks and bridge posts is either one or the other: they seem too big to be tags but not public enough to be street art. Occasionally the council sends a batch of these kids down to paint over all the tags/art/graffiti, thereby leaving a beautiful new white canvas for the next lot.
Whenever I see a fresh batch of cans my brain automatically starts singing the Arctic Monkey’s Riot Van. They just wind the coppers up. Ask why they don’t catch proper crooks.