What does this blue symbol mean?

I have just done a variety of events in the Straits of Devastation with 30-40 random people and upon finishing I noticed that a few of these had a blue symbol above their heads, kind of like an arrow pointing down at a chevon:

I am assuming that this is something to do with the auto-grouping feature in Guild Wars 2. What does this blue symbol mean? Is this something that is assigned by the game or player assigned?

Solution 1:

That symbol marks someone as a Commander in WvW and PvE. It is obtained by purchasing the Commander's Compendium for 100 gold from a trainer.

As a commander, you are given access to a special set of tools for use in WvW/PvE, from the Wiki:

• /squadinfo will show the names of players in the squad and the amount of supply they are carrying. This command only takes squad members into account.
• /supplyinfo will show the names of adjacent allies and the amount of supply they are carrying. This command is not limited to squad members, but its radius is very small.
• ALT+Mouse1 opens a context menu for adding special order waypoints, to mark locations for attacks, defense, and rally points. These special waypoints are visible to squad members.

The symbol also appears on the in-game map, making it much easier for other players to spot, in most cases, the location of the zerg for their team.