On a couple of recent MetroRail rides I noted that the wall signs at Rosslyn are so filthy that they cannot be read by passengers in the train. I think this could be remedied with a little soap and water. See photos below:
Here's one of the filthy signs. From a moving train, this cannot be read.
This may be a problem in other stations, particularly those with center platforms, where the dust from the trains can easily adhere to these signs and where they would be harder to service, since they are over the tracks. If you know of any, feel free to mention in the comments.
Steve Offutt, Arlington