Gameplay

Vigilante

From Halopedia, the Halo wiki

Vigilante is an achievement in Halo 2 (Windows Vista). It is worth 10 Gamerpoints and is earned when the player stops an enemy's Killing Spree, similar to the Killjoy medal from Halo 3.

It is represented by an octagon with a green four-pointed star and a bulls-eye on the interior.