The Doom logo is a famous logo used throughout the Doom franchise.
The logo can be found here.
The upper part of the logo is blue, with mechanical parts, and the lower part is brown, with a natural/organic appearance. These "mechanical/organic" contrasts are part of an artistic concept. Some parts of the game, such as the Cyberdemon or the three episodes scenarios, have the same characteristics: Phobos is completely technological, Deimos is half-tech and half-demonish and Hell is completely demonish.
The logo was used in Doom, Doom II, The Lost Episodes of Doom, The Ultimate Doom, Master Levels for Doom II, Final Doom, Doom RPG, the Doom novels, and the Doom comic. In Doom 64, the logo was given a more three-dimensional effect.
Doom 3 version
In Doom 3, Doom 3: Resurrection of Evil, Doom, The Boardgame, and Doom 3: Worlds on Fire, the logo is modified from the original, but still bears a strong resemblance to the outline and coloring of the original logo.
Doom movie version
In the Doom movie, the logo is colored black from top to bottom.
Doom 4 version
A variation of the Doom logo has been found on the id Software website, which has been speculated as the Doom 4 logo. It has a similar form as the classic logo but the letters appear to be made out of rock, with lighter colored rock on top, darker on the bottom. A fire effect has also been added to the background.