From Halopedia, the Halo wiki
Triple Double is a multiplayer medal available in Halo: Reach, Halo: The Master Chief Collection and Halo 5: Guardians. It is earned by finishing a game with double-digit kills, assists, and headshots. In Halo: Reach is represented by a triangle with an equal sign in the middle, on top of a blue circle. In 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 as a blue rimmed, blue and red colored square with a side view of a Mjolnir Mark VI helmet in the middle.
In Halo: Reach the medal does not appear in-game and can only be viewed on Bungie.net. In The Master Chief Collection it appears in-game for the first time, and can be earned in all five versions of multiplayer.
On March 31, 2012 Bungie.net ceased updating Halo game stats and player records, transferring all record-keeping responsibilities to Halo Waypoint. As Triple Double awards for Halo: Reach could only be viewed on the site, it is effectively no longer awarded in that game.