Rising Storm/Red Orchestra 2 Multiplayer had Steam trading card support added on 16 July 2013. There are 10 cards in the series, and you'll receive 5 cards at random for purchasing and playing the game.
Unlike with most other games, purchasing and playing either Rising Storm or Red Orchestra 2 will drop cards from this set.
Rising Storm 2: Vietnam also features trading card support.
Trading Cards
Foil Cards
Badges
Booster Pack
Emoticons
Profile Backgrounds