I have been scanning the internet for a while now, but I still cannot find the origin of this poster, which is necessary for a bibliography. Any help would be greatly appreciated and sorry if this is in the wrong place.
It's a political poster of anonymous authorship, referencing both the black power salute at the '68 Olympics and activist Fred Hampton's quote:
But that’s alright, because we said even before this happened, and we’re going to say it after this and after I’m locked up and after everybody’s locked up, that you can jail revolutionaries, but you can’t jail the revolution.
It was in protest to the imprisonment of the Chicago Seven (also the Conspiracy Seven or Conspiracy Eight). You can see a version of the full poster here.