Further up Columbia Pike in Arlington are more banners. These banners have been here for several years, and Arlington changes the banner throughout the year to commemorate different celebrations and holidays. These patriotic flags generally go up for summer (Memorial Day, Flag Day, Independence Day are among the summer holidays). However, back in September 01, these flags stayed up much longer.(I don't remember if for the entire year or until after Thanksgiving.) Columbia Pike, you see, is the road leading up to the Pentagon. Also, since then the two flag banners at each end never change. It's likely an oblique tribute.
On the picture, the odd thing here is cross the street, the flag banner is upside down. If that was the US Flag, it would signal distress. Of course, that is not the flag, but being upside down brings attention to itself.