This item is a PvP reward, and can be purchased for 8000 from <Officer Accessories Quartermaster> in Hall of Legends.
As the cooldown is only 2 minutes (compared to with a cooldown of 5 minutes) and it has resilience which will keep you alive longer and reduce burst damage on you, it would be a good idea to get this once you hit 70 if you use your Insignia a lot.
Though it is mostly aimed for PvP combat, it is useful for the Rage Winterchill and Archimonde fights in Mount Hyjal as both of these bosses have abilities which result in the player becoming frozen or feared. It is common for guilds to require this item for these bosses for this reason.
Technically there are 9 different versions of this item (one for each class), but they all have the same stats.