New York City wants to teach residents to be responsible with water by turning water towers into public works of art. The campaign is called Word Above The Street, it will take place in 2013 and will feature artworks from a myriad of artists, both famous and not, most of which will have a (surprise!) water theme.
It's a great way to add color to the urban cityscape and (legally) let people see your serious art skills, but I think the water conservation aspect will require a street team to spread the message.
Link --via DesignTAXI
There's a program running in a couple of cities in Australia, (Brisbane & Melbourne) to paint Traffic Signal Boxes. So rather than have a large ugly grey box at any set of Traffic Lights, there's a colourful bit of art.