Insert my VERY first trip to DC somewhere between the west extension of K Route Orange Line (Ballston to Vienna) and the North extension of B Route Red Line (Silver Spring to Wheaton). Sometime in March or April of 1988 (I went to Baltimore in June of the same year, albeit NOT by Amtrak this time... and that was the last I'd see of Baltimore other than passing through until December 1997).
Anyways, I recall seeing a flipdot sign, and asked my father, "Why do the trains here have bus signs?" (I was only six years old, gimme a break). However, I think I do recall seeing a rollsign somewhere... I'd likened it to the rollsigns on SEPTA's RTS II, Flxible buses, and the Kawasaki LRVs. I can't recall exactly where I saw the sign; but the only stations I even SAW that day were: Union Station, Judiciary Square, Gallery Place (not sure if the Chinatown suffix existed yet), Metro Center, Federal Triangle, and Smithsonian. I DON'T recall which train we boarded at Metro Center, but I THINK it was Blue. However, we'd just missed a train ahead of us, and saw a train going past us towards I Street Corridor and VA... I think THAT's where I saw the flipdot... so the rollsign might have been my Red train.
Of interesting note, I had a pamphlet about the Metro system that showed the downtown stations... Archives had not its suffix, and I think they forgot L'Enfant Plaza on this... that, or the map of downtown was small enough to not include 7th & D SW.
And back in 1995 is when I got the Guide to the Metro System that had mentioned something about a "Saturday Express"... this was AFTER Anacostia opened... and until this point, I'd NO idea how huge the system had become (How far in the dark was I? I'd never even HEARD of Federal Center SW, nor knew of the suffixes added to some stations)