Rockstar
This is how you solve a problem artistically. Instead of banning chewing gum (hello Singapore, 1992-2004), Hubba Bubba collaborated with DDB advertising, Sydney to tackle the problem of chewing gum on the streets by putting up fun, interactive "chew by number" posters that use different flavours of chewing gum as the colour palette, thus encouraging people to become artists rather than litterers.

Each poster has a color map and numbered regions so you would know where to stick your gum. Ingenious :)