Changing team name that appears in stats in CS:GO
The in-game stats window in Counter-Strike: Global Offensive includes a highlighted prefix before certain players's names. It seems to be a team/clan tag like players sometimes include directly in their Steam display names.
I went through the in-game settings but I don't see any place to specify this. There's no option to type in a type in a team name, or any way to join a team.
How do I change the my team name?
The team names are representative of the groups that you belong to on Steam.
In order to change the team name you must belong to any group that has a tag. You can find these groups under the Community section of your Steam Interface. Many public groups are open to join with little hassle. Simply click the join group link on the right hand side.
After you sign up to any of these groups you can change your settings in game to the tag you want. In game go to "Settings menu" → "Game Settings" → "Team" → "Steam Group Clan Tag":
Do you belong to more than one group in Steam? The groups don't have to be CS:GO specific to show the tag.