There are (at least) two artists named CB4:

CB4 (American)

CB4 was a fictional rap group from the 1993 parody, rapumentary and comedy film named CB4. Named after the prison block the band was formed in (Cell Block 4), the movie parodies the rap group N.W.A. among other gangsta rap aspects. It was directed by Tamra Davis and can be seen as rap music's equivalent to This Is Spinal Tap.

CB4 (Balkan)

CB4 is a Serbian rap group, with an album entitled Ol' Skul Shit. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.