Step 1: Material
Plastic suitable for the type of cutting you will do. (The more intricate your design, the easier the plastic needs to be to cut)
A knife or set of knives. I got a set of Xacto knives with a bunch of blades for $3 at Menards.
A template for cutting.
Spray paint for coloring.
Step 2: The first step.
Since my project required 2 layers,one as a background, one as the shape and the letters, I cut the background slightly larger than the foreground and left it solid. For the foreground I cut out around the letters, but left the top and bottom attatched to the "body" of Cthulhu to make it easier to glue. I did all the cutting while watching "In Bruges" (great movie, by the way)
Step 3: Painting.
Step 4: Final step
Once you are done, find a way to attatch it to your vehicle of choice. Glue, magnets, some kind of adhesive foam backing, its your choice. Once I get a car, this thing is definitely going on there, and I'll see if I can find some other H.P Lovecraft fans.