What does the 2nd line mean? Rogue Squadron in this screen shot. And more importantly how does it get set?
This is the clan that the person is a member of. This can't be set up in the game itself, instead you need to log onto the bungie website here:
There is no in game support for clans apart from this line in the emblem. There are no ways to talk to clan members through the game or see which of them are online (except through having them on your friends list, etc.)