Killzone 2 Badge System:

Rather than adhere to a rigid character class system, Killzone 2’s online mode allows the player to mix abilities from different roles to better suit his / her preferred style of play. Abilities are represented by badges: the primary badge defines the main role of the player character, as well as its outward appearance, while the secondary badge serves as a complementary ability that enhances the main role.
Although their player characters look different, both Helghast and ISA factions have the same set of roles and badges to choose from. Here they are, from left to right:

Rifleman:
The default multiplayer character is assigned when no primary badge is selected. A secondary badge may still be added. Riflemen can start with most weapons, except for the specialized ones.

Engineer:
Primary badge ability: Sets up an automated turret which targets the enemy.
Secondary badge ability: Repairs ammunition dispensers, mounted guns,and automated turrets.

Medic:
Primary badge ability: Revives downed team mates.
Secondary badge ability: Throws a health pack, which can be picked up by other players.

Scout:
Primary badge ability: Uses a cloaking suit to become near-invisible.
Secondary badge ability: Tags all on-screen enemy players with a hidden marker, which broadcasts their coordinates to team mates.

Assault:
Primary badge ability: Dons heavy armour twice as strong as normal.
Secondary badge ability: Temporarily boosts running speed.

Tactician:
Primary badge ability: Throws a coloured smoke grenade, which serves as a spawn point.
Secondary badge ability: Requests air support from a sentry bot which targets the enemy.

Saboteur:
Primary badge ability: Assumes the disguise of a randomly selected enemy player.
Secondary badge ability: Throws a sticky, proximity-activated C-4 charge.

Some multiplayer screens from Killzone