On the Scorpion Tank in Halo 2, there is a picture on the front left tread. The piece varies based on which level is being played in the campaign, or it may be random or determined by some other factor in multiplayer. The picture switches between being a hand, a lightning bolt, a chess knight, and two circle based images.The chess knight is on the Scorpion's tread in the Halo 2 manual.
