Billboards are few and far between in the capitol of the United States, but the ones that exist are huge and in your face (most of them are outside of the district). Wallscapes (billboards on the sides of buildings) are also popular because of the limited availability of traditional billboards.
Washington, DC Billboard Advertising Data:
Washington, DC Billboard Advertising Rates (average per location per 4 weeks):
Map of Washington, DC Billboards: