Check out this App developed by 1AM in San Francisco.
1AM Mobile is a free and community driven photography app that celebrates art in the streets by letting members capture and share what they see in the streets and also view and share what others members have contributed. In essence, 1AM Mobile will tell you what’s up in the streets and let you take part in documenting street art history.
Just search 1:AM in the iTunes App store and it’s the first result displayed.
More info: