Serious Sam HD: The Second Encounter had Steam trading card support added on 18 March 2016. There are 8 cards in the series, and you'll receive 4 cards at random for purchasing and playing the game.
Other games in the series, Serious Sam HD: The First Encounter, Serious Sam 3: BFE, Serious Sam 4, Serious Sam: Siberian Mayhem, Serious Sam: Kamikaze Attack! and Serious Sam Bogus Detour also have Steam trading card support.
Trading Cards
Foil Cards
Badges
Booster Pack
Emoticons
Profile Backgrounds