I've got access to a vinyl cutter at work, so I whipped up a Ball Python silhouette and cut it into white reflective vinyl. So in the daytime it's nearly invisible on my white car, but at night... it lights up like a roadsign!
http://i29.tinypic.com/25ujvh2.jpg
I just love working with vinyl - mostly I just do dogs, but I had to try a snake. :)
A custom Aussie decal I did for a friend:
http://i26.tinypic.com/i75r0n.jpg
And the dobe I have on my car - my actual silhouette for Dobermans is different, but this one is a custom decal of my own dobe, Ilsa:
http://i25.tinypic.com/29vb9lw.jpg