We contacted Fallout 3's PR people and they sent us several images of various ads found in the city's subway. We didn't receive any details about which stations these images were taken from, but we've placed all the pictures we got in the gallery below.
Update: Pete Hines, Fallout 3's product manager, wrote us to say the ads are currently only at the Metro Center station. He explains the company took over all the ad space there for the month, adding that DC residents will start seeing bus and bus shelter ads in the near future. The company plans to promote Fallout 3 in other US cities soon.