The rumor is that they were shooting promotional footage for something or other on the History Channel

But it looked to me like they were signaling an alien lifeforms on a spaceship. I got to work a little before 7:00 this morning and there were 50 people milling around between the Capitol Columns and the small parking lot adjacent. They ran huge cables everywhere,set up  banks of 10 foot parabolic reflectors, a huge boom, enough light to light the ellipse in the dark, and, get this, a food service. I was impressed but I wasn't hungry. They went about their business all day and were still there when I left just after 4:00.