Successfully complete the indicated task to unlock the corresponding stamp:

Kit specific
Knife Efficiency: Kill four players with melee weapons.
Explosives Efficiency: Kill four enemies with grenades or explosives.
AT Efficiency: Kill four vehicles with recoilless rifle.
Rifle Grenade Efficiency: Kill four enemies with rifle grenades.
Pistol Efficiency: Kill four enemies with a pistol.
Rifle Efficiency: Kill four enemies with a semi-automatic rifle.
SMG Efficiency: Kill four enemies with a submachine gun.
Sniper Efficiency: Kill four enemies with a scoped rifle.

Vehicle specific
Vehicle Efficiency: Destroy six vehicles in any fashion.
Jeep Efficiency: Get four kills with a car.
Tank Efficiency: Get four kills with a tank.
Plane Efficiency: Get five kills with a fighter plane.
Boat Efficiency: Get two kills with a landing craft.
HMG Efficiency: Get four kills with a heavy machine gun.
Air Defense Efficiency: Kill two planes with an anti aircraft gun.
Bombing Efficiency: Kill four enemies with air raids.

Teamplay
Air Superiority: Shoot down three bombers.
Vehicle Assist Efficiency: Get five vehicle assist kills.
Leatherneck: Kill at least twenty enemies.
Defender Efficiency: Defend five flags.
Attacker Efficiency: Capture five enemy flags.
Best Squad: Be the best squad of the round.
Teamplayer: Get ten squad assists.
Squad Excellence: Each squad member gets any one stamp and kills ten enemies.