Here's an idea for people who want to use a sticker but don't like the idea of permanently sticking one to their vehicle.

Turn your sticker into a magnet.  Everyone gets those magnetic advertisements and magnetic calendars.  Most of these are garbage and promptly get thrown away.  You might even have a few stuck to your refrigerator right now.  Put those magnets to good use by using them as a base for your cool stickers. 

Simply find a magnet large enough to accommodate the sticker of choice.  Stick the sticker to the magnet, then cut the magnet to fit the shape of the sticker.  Now you can attach the "sticker magnet" to your painted metal surfaces instead of slapping the sticker to it. 

The benefit here is that you're able to remove or adjust the sticker without ripping it off the paint, possibly damaging the painted surface.  You get the sticker without commitment.  You don't have to make a permanent decision as where to stick that sticker.  You can easily remove it and put it somewhere else, or re-arrange your sticker collection.  You have a magnet that can be slapped on your vehicle for the trail run, and then removed when it's time to clean up the vehicle, apply wax to the paint or head back to the office.  Additionally, when you need larger magnets, you can purchase magnetic sheets for your monster sized stickers.