Obama's office is, until January, across the street from us. Aren't we cool? The impression I have is that the way they're protecting him is by maintaining a bumper-to-bumper caravan of Federal Protective Service vehicles radiating three blocks in every direction from the building.
I find it interesting that the Secret Service wear shades. Maybe so people can't see their eyes? It's odd.
Yes, it's about not being able to see their eyes. The idea being that you don't want a close-quarters attacker to know where the agents are looking at a given moment.