Stating The Obvious

Public places always need to have rules in place for citizens to abide by. No dogs, glass bottles, and obscenities, (actually misspelled on this sign) are all common and reasonable rules. But no gang activity? Isn't that a bit self-evident. And does anyone believe putting it on a sign will do anything to curb gang activities? Is the idea that gang members will see the sign and go "alright guys, we need to break it up and play a game of bridge instead, the sign says no gang activity."