We used "покеда" (afaik, it's spelled with "o") quite often when we were kids. It's just informal and/or colloquial and hardly has anything to do with a criminal slang. I don't think it belongs to any particular sub-culture either because we were pretty much mainstream. "Покедова" was not popular among my peers, I guess it's either one or the other.

Anyway, it's always safer to use a universal "пока". "Покеда" and "покедова" are just a little silly. ))