There are standard designs you can get in stores for vinyl decals. However, if you are into designing graphics or would want to have your own graphic design made as a decal, you can do so by doing custom vinyl decal printing.

You can either do it by yourself, like buying the blank vinyl decal sheet, or have a professional printer to do it for you.

http://www.visigraph.com/custom-decals-stickers-magnets-and-labels/custom-vinyl-transparent-decals-stickers/