Bro Hammer
From Halopedia, the Halo wiki
Brohammer
Brohammer is an achievement in Halo: Combat Evolved Anniversary and Halo: The Master Chief Collection. It is awarded for completing any level cooperatively on Legendary difficulty. It is worth 50 gamerpoints in Halo: CEA and 10 in Master Chief Collection. Receiving this achievement also unlocks the "Standard Operating Brocedure" and "Brovershield" achievements if the player hasn't completed a level cooperatively on Normal or Heroic, respectively.
It is represented by two Sangheili skulls over the Heroic difficulty shield.
Trivia
The achievement is a reference to Carol Rawley's callsign, "Foehammer".
