Doom 3 Easter Egg - Shadows of the Past

In two parts of the game that I can remember there are large tablets that the archeologists used to discover more about the Soul Cube. On one, the fourth tablet (the one on your left in the room where they are on display where the audio description is being played), it depecits hero of the alien culture holding the Soul Cube. This is actually a modified form of the old promotional poster that came with the original Doom game, but it was reversed and has fewer details.