From Halopedia, the Halo wiki
Nameplates are small icons seen in pre and post-game lobbies showing player's Gamertags that can be customized depending on certain requirements. Although nameplate emblems have existed since Halo 2 and Halo 3 in the form of small Seventh Column symbols or the Bungie logo, they would not be customizable until Halo: Reach. Nameplates were first mentioned early 2010, when Halo 2 was being shut down and again when Halo PC users were told to keep their CD codes.
Players could customize their nameplates by signing up as Bungie.net users until March 31, 2012 when Bungie.net transferred all record-keeping responsibilities to Halo Waypoint and this capability was lost. Halo Waypoint did not incorporate nameplate functionality, and players are effectively stuck with whichever nameplate they currently have.
There are only three nameplates in Halo 2.
There are only four nameplates in Halo 3:
There are thirteen nameplates available in Reach. Nameplates were originally configurable by logging in to Bungie.net.:
Halo: The Master Chief Collection