just see who has the best connection

At the very beginning of a game, usually everyones drops to 1 bar, except 1 person who stays at 4, that's the host.

On the top right corner where it's says starting game and stuff like that, at one point when the host leaves it will say choosing best host. Whoever's name appears on the top of the list of everyone before the game starts is the host. It's been like that since cod 4, always been helpful. Best way of telling who is the host. Hope this helped you out.

Just like one other person has stated. In the map loading screen at the lower right it will say "awaiting challenge" if it doesn't say it then your not the host