DESIGN I have played Dungeon & Dragons with my friends for a long time, and I thought a d20 was the perfect tool to play with the 3D features in Photoshop. "DM" stands for Dungeon Master and is just the person that facilitates the game. This play on words is fairly common on Dungeon & Dragons merchandise.
PHOTOSHOP I played with the 3D workspace at length while making the die. I tried a lot of materials until I found one that mimicked the real-life texture of dice. I added a gradient and then used the lighting features to add shadows that followed the same angle as the gradient pattern. I softened the shadow and rendered the object.
I then put a layer behind the object to create a background and then added a vignette to the layer using Camera Raw. Finally, I added the text. I found an old-timey font and then used layer styles to add the outer shadow around all of the text and the stroke around DM to emphasize it.