After a little googling around the web, I think it's more of an urban legend than anything else. It has a lot of the earmarks of folklore: e.g., differing locales (Africa, the Americas, Australia) and participants (Africans, Native Americans, Aborigines [on walkabout]), absolutely no citations, when, where, who ... The context is a vaguely Christian one (I saw one person saying it was an Orthodox bishop's favorite saying). Here's an example: link. In it's poresent form it seems to go back no further than the '80s.

Ceci n'est pas un seing.