BB just means BadBoy. Basically, as you start conquering and annexing factions, your BadBoy meter goes up. The higher it is, the higher the chance that a gigantic coalition of the other faction pops up. You don't want that to happen. As to where it can be found, no idea myself. I only have EU: Rome and for the love of the Gods, I can't find it.
EDIT: ALright, I think the BB indicator is on the diplomacy screen of Rome. Will check that out tonight or tomorrow.