Pretty positive they're free for open use. Like to remind y'all that though I agree 100%, putting said stickers on Bummers (Dummers/Hummers) et all that are not yours is defacement of property and some people will go as far as to say it's vandalism/libel (because it's in written word that their brand new, shiny gashog is Dummer) and you may be taken to court.
This is as illegal as piracy and vandalism becasuse I'm sure they'd be the first to tell you they bought their monstrosity and the gas to run it with their own hard-earned American dollars, and soldiers, babies, and maybe even Jesus died to give them the right to drive their almost-scaled-down version of an Abrams tank.
How can you, a cyclist, appreciate the hard work and labor that went into their eyesore?
I have a good idea that these images are out there for open use so modernday punk kids who don't care about the legal implications above can print them off and slap 'em on cars etc and without copyright "ownership" of the image, the site can't be blamed. Also, it makes it easier to get the 'word' out there when people don't have to pay for it.
Food for thought.