The riders of DC's Metro system aren't always known for good rider etiquette. Though you can't see in the photo, this metro car is fairly full (there are no empty seats and some people are standing). To discourage people from sitting next to them, people often sit their bags on the seat next to them or sit on the aisle side of the seat. This forces people who want to sit to ask them to move their bag or move over, which most people usually will do. I've never seen someone say no. I just think it is rude to force people to have to ask to sit. Interestingly, many times these people will be reading the Bible as they hog two seats.
