well, it's from a betting game called "jogo do bicho"(animal game) in which numbers are correlated to animals. 24 is the number of the deer or "veado" in portuguese which also happens to be a pejorative brazilian slang for gay men. there's another theory in which 24 sounds like "coming in all fours" in portuguese. anyway, the origins are uncertain, but the symbolism is common knowledge around here.