Dog Tags are small identification badges that soldiers normally carry around their neck in the field of battle.
In Crysis 2 multiplayer they serve two functions:
First, they serve as a icon for a players profile. Every player can choose between a wide variety of dog tags on initial startup; most of them are national flags. As players progress through multiplayer, they can unlock new dog tags to use.
Second, players drop their dog tags upon death in a multiplayer game. They can be collected by the player who killed them. Collecting dog tags unlocks support-measures such as the Orbital Strike. Players who collect more dog tags in a single life will unlock more powerful support bonuses.
There are two special Crysis 2 dog tag frames. The Platinum dog tag frame, which is available through purchase of the Limited Edition or Maximum Edition, and the Golden dog tag frame, which was only available through pre-order from Origin, but is now available with the Maximum Edition.
Dog tags are also present in Crysis 3.