A small circle like the "mumble recommended or not" circle, that is green yellow or red. So if someone knows that is not very good, or wants to try a map or a class for the 1st time will go in green marked lobbies, and a good player that wants to play his main class in a well-knowed map will join a red marked lobby. This suggested skill level indicator is chosen by the lobby leader when the lobby is created, but doesn't create any real restriction: is the own player that choose if a red lobby will be good for him or not. But if he joins, he's expected to play very very well.