Hedgemony discovered what appears to be a totem pole-like images of creatures in certain building textures.
"The textures are like totem poles that have several faces and creatures running vertically up the walls. These sobs are there and I'm not majing this up.Link to original forum post
At the beginning of SC they can be found in the archway of the first structure that you come across. If you go in front of this structure by going into the water, then turn to face the building they are inside the archway going back onto land. Standing in the archway look at the center of the building then zoom in with your pistol and follow the textures in the middle of the wall. They are there and on the roof as well.
On two betrayals they can be found in the tunnels before Final Run commences. They are on the walls before you make a left turn to get outside into the snow. Once again look at the middle of the wall and they will be there. They are not that obvious but can be recognised by what looks like arrow shapes pointing upward. Sounds nuts but it's really hard to describe.
The reason these are important is because they are not normal textures. They have animals and faces all lined above each other.
On the level halo they are on the buildings that fire the pulses. If you go up the ramp to this building then turn left you will see a concrete box/square. Jump onto the box and face towards the building, the texture is right in front of you. Zoom in to the wall and you can make them out. Do this now and capture them. Post them and give me some love! "
My opinion is that either 1) the artists at Bungie were being very clever and teasing us or 2) this is what happens when a texture is used side-by-side but flipped. The 'seam' of the two textures mating creates these funny looking faces.
Used my Xbox Dev kit to remove the weapon.°
°Haha fooled ya!