Large, very visible signs on the walls of the stations that include the name of the station itself, but also the name of the previous station and the next station on the line (with an arrow pointing in the direction of travel). You can see this in Japanese train stations, and it is a huge time-saver!
The signs should be easily visible from any seat on the train. Lights, and bright colors would help as well. Even as a native DC resident, I sometimes lose track of where I am on the line. It would really help to have very visible, very helpful signs.