These are made of vehicle-safe magnetic vinyl. It's the same kind of signage you see on pizza delivery cars. As long as the car surface and magnet are kept clean there is no risk to the car's finish. The magnets also have a firm grip as long as the entire magnet is in contact with a metallic surface. I drive with one at 80 mph almost daily with no problem. The vinyl is made for outdoor use and can be displayed in daytime heat, cold weather or snow and rain, but if it is stored when not in use the lifespan of a vinyl sign can be extended.

Normally the larger sizes sell for $12-$20 each. However I have extras from Botcon, so I'm blowing them out on ebay. I have a set of 6, both G1 style factions in 3 sizes, with a staring bid of $15. (click link here)

I make other designs as self-adhesive labels or magnets, and can do custom work from my online store here. (click link here)