Steam reward

Steam rewards are attainable items awarded for players who play Halo games on Steam. They are commonly divided into Trading Cards, Emoticons and desktop wallpapers. Currently, the only Halo games to support Steam Rewards are Halo Wars: Definitive Edition and Halo: Spartan Assault.

Halo: Spartan Assault
The rewards for Halo: Spartan Assault can be found here.

Halo Wars: Definitive Edition
The rewards for Halo Wars: Definitive Edition can be found here.