Left 4 Dead 2 had Steam trading card support added after the initial test batch of trading cards, but still during the beta phase, on 6 June 2013. There are 8 cards in the series, and you'll receive 4 cards at random for purchasing and playing the game.
Trading Cards
Foil Cards
Badges
Level 1
Patient Zero
Patient Zero
Level 2
Infection
Infection
Level 3
Outbreak
Outbreak
Level 4
Epidemic
Epidemic
Level 5
Pandemic
Pandemic
Foil Badge
Extinction Event
Extinction Event
Booster Pack
Emoticons
:boomer:
(common)
(common)
:health:
(common)
(common)
:tank:
(common)
(common)
:witch:
(uncommon)
(uncommon)
:chainsaw:
(rare)
(rare)
Profile Backgrounds
4
(common)
(common)
Cemetery
(common)
(common)
The Quarter
(common)
(common)
The Hand
(uncommon)
(uncommon)
Midnight Riders
(rare)
(rare)