Originally Posted by The Weltman
It depends on what you mean by team. If you mean that you want to play on Horde/Barbarians then yes, you must select this at registration. Otherwise it is not important as long as your team of friends all sign up for the same group.
For a special M.O.S. card, you must ask your command staff at the game.
By team I meant the smaller group of people within a gang, like these teams, for example. LL5: The Horde teams by gang