Wallet Card at an Anti-Apartheid rally sign

This may be the coolest find yet for my wallet card. I had read about how an ad for a 1980 anti-nuclear concert was occasionally visible at the Herald Square subway station. I didn't find that but I found something even older, and at least as relevant - an ad for a 1976 anti-apartheid rally at Herald Square and subsequent march to South African Airlines headquarters. It would appear that at least at this subway station the MTA has not removed historically relevant flyers when switching out advertisements.