alt Hacker NewsAssuming you mean one of these guys:
https://cptdb.ca/wiki/images/6/60/San_Francisco_MUNI_8001-a....
https://cptdb.ca/wiki/index.php/File:San_Francisco_MUNI_8110...
The signs made quite a racket, but so did the buses (well, the first model I linked to).
Fun fact: When Muni first rolled out the digital signs on their newer Bredas the set the signs to rotate through three different pieces of information. So for 2/3 of the time you had no indication of where the train was headed.
Bonus fun fact: the cloth rolls have a variety of routes and destinations that never came to be.
When I was a kid, DART (a not-quite-metro rapid transit thing in Dublin) trains had printed maps with LEDs for each station; they were green until the train passed them, then turned red. This seemed like absolute magic to me at the time.
When a branch line was added, these displays were updated, though they weren’t put in the newer rolling stock. Then another station was opened on the existing line, and they just switched them off. They’re still present on some trains, but haven’t done anything in 15 years. They’ll finally presumably go away in the next year or so, as the ‘80s rolling stock they’re found in is due to be retired. I’ll kind of miss them.