Looks like a warning/disclaimer at the bottom of this page
http://www.changingtheclimate.com/bumpersticker.html
NOTICE: TAG ONLY BUMPERS, DO NOT TAG A PAINTED SURFACE! Plastic type bumpers should not be tagged as people have claimed that the finish can be marred by the bumper sticker. Please put the sticker on the bottom of the rear window of such SUV's. Make sure you put it on the bottom of the window so as to not obstruct the rear view vision of the driver. Also note the following. Although I have tagged hundreds of SUV's without incident,
you do take a risk and should be aware that there are crazy violent people out there and if you cross one who happens to own the SUV you are tagging things could get ugly. I have a report of one person who took up the sport of big game SUV tagging getting into a fight with an enraged SUV owner and getting hurt, so you can be risking a serious confrontation with the owner of a tagged SUV. You have to decide if you want to take this chance. But remember, the founding fathers didn't shy away from a skirmish. We are at an environmental Bunker Hill! SPREAD THE WORD AND CHANGE THE WORLD!