There's an app for NYC called Can I Park Here[1]. It does location queries against the NYC DOT parking regulations database[2]. Perhaps something similar exists for DC?

[1]: http://www.nytimes.com/2012/01/22/nyregion/iphone-app-tells-...

[2]: http://a841-dotvweb01.nyc.gov/ParkingRegs/ViewController/Loc...