A logo of the [[Gears of War]] franchise, consisting of a skull in the middle of a gear.  May not actually be crimson in any given image.  Also applies to parodies where something else (e.g. [[Kochiya_Sanae|Sanae's]] [[hair_ornament|frog]]) is in the gear.

See also:
http://gearsofwar.wikia.com/wiki/Crimson_Omen
crimson omen