The Old Guard is the US 3rd Infantry Regiment. They are a ceremonial unit, primarily concerned with guarding the President and important locations around the Capitol. Their most visible post is at the Tomb of the Unknown Soldier.
While the rest of the Capitol was shutting down yesterday for the big blizzard, and the State Department couldn't make its usual Friday afternoon email dump, the soldiers of the Old Guard were standing their post.
I will guard everything within the limits of my post and quit my post only when properly relieved.