Rumor confirmed by WMATAGMOAGH (Oren). Thank you.
They looked bigger in 1998, but then again, I wasn't at Stadium-Armory... I was at Rosslyn (I was sleeping when we went through Stad-Arm). They also seemed harder to see (of course, I was in the middle of the platform, but even at S-A, I was in the middle and could see the smaller signs fine)
Hm... imagine the RED LINE having them... Maybe just at Metro Center, or at the "midway" terminals, to indicate if the train's turning back or not. By that logic, then Mt Vernon Sq-7th St needs one also.