"Personalized license plates might seem like a harmless accessory, but they could make you a more likely target for criminals. Why? Because they communicate much more than the written message. "Personalized plates indicate that the person bearing them wants to be noticed," says Phil Messina, a retired New York City police officer and founder of a self-defense school in Lindenhurst, N.Y. "The downside of doing things that tend to 'get you noticed' is that they can get you noticed by the wrong kind of people."

Consumer advocate Tim Duffy agrees, pointing out that plates indicating the driver is a woman or a senior citizen or both -- as in "Katie's Grandma" -- are especially problematic. Spotting one of these plates in a parking lot, a mugger may hide behind or near the car, waiting for the driver to return. "You don't want to be a victim of a crime," Duffy says, "and you don't want to make it easier for someone to commit a crime."