Beware of the car with bumper stickers, trinkets dangling from the mirror and decals on the windows, even if they seem as benign as a college logo. According to a new study, drivers in cars festooned with personalized markers tend to drive more aggressively and express their anger physically on the road.

Researchers at Colorado State University established a link between bumper stickers and road rage. The more bumper stickers and other personal expressions on a car, the greater the likelihood that the drivers would use their vehicle to cut off, tailgate or even ram another car. The tendency to act aggressively proved independent of the bumper stickers’ messages; drivers with positive or neutral messages (such as “I Brake for Animals”) were just as likely to act as dangerously as those with negative or aggressive messages (such as “Dropkick Bush”). Drivers in cars without bumper stickers also got angry behind the wheel, but they didn’t express their anger in physically threatening ways.

The researchers interpreted bumper stickers, window decals and mirror decorations as “territorial markers.” Drivers who personalize their cars with stickers and decorations mark their cars as “primary territory,” and they take action to defend it—even on “public territory” such as a roadway, where social norms would dictate a less aggressive response. The study appeared in the Journal of Applied Social Psychology.