Graffiti and other notes left on walls were used for sharing updates, spreading rumors, and tracking accounts
Cool that graffiti has kind of changed in a way where people will tag pretty much whatever just with their name when it used to be more informative. That informative part of street art I think it has been taken by flyers or posters that will have updates or messages. But more and more these days I am seeing explicitly politic graffiti around witch seems a bit closer to it's original use.