The Triple Double medal is a multiplayer medal available in Halo: Reach and Halo: The Master Chief Collection. It is obtained by finishing a game with double-digit kills, assists, and headshots (sniper headshot medals also count).
In Halo: Reach, it's represented by a triangle with an equal sign in the middle, on top of a blue circle. In Halo: The Master Chief Collection, the triangle is black and grey and is imposed on a black and red hexagon. In Halo 5: Guardians, it is represented by a blue rimmed, blue and red colored square with a side view of John-117 custom MJOLNIR/Mark VI helmet in the middle.