Driving is one of the most enjoyable experiences of modern life , and sometimes, aggressive drivers ruin it for the rest of us. Some studies show that aggressive driving might be responsible for up to two-thirds of all U.S. traffic accidents that involve injuries. Thankfully, there’s now a way to spot them… look for bumper stickers.

That’s the conclusion of a recent study by Colorado State University social psychologist William Szlemko. He found that drivers of cars with bumper stickers, window decals, personalized license plates and other “territorial markers” are far more likely to express “road rage” and aggressive behavior than those without the markers. The best part: It doesn’t seem to matter what the message on the sticker is, “Peace and Love” or “Bomb ‘em All”, just the fact that a person has stickers or markers makes road rage more likely.

Szlemko and his colleagues concluded that regular drivers get mad too, they just don’t express it the way drivers with bumper stickers do. They theorize that the key to the whole issue lies in territoriality. “Territoriality is hard-wired into our ancestors from tens of thousands of years ago,” said Paul Bell, a co-author of the study at Colorado State. “Animals are territorial because it had survival value. If you could keep others away from your hunting groups, you had more game to spear . . . it becomes part of the biology.”

That comes into play when aggressive drivers mark their territory by putting bumper stickers or other identifying markers on their car. Then they’re more likely to treat the road their driving on as their own personal space.