I've always heard that any markings on the car make you a target. For example having the sticker your auto insurance agent gives you invites people who are looking to commit insurance fraud since they know you have an insurance policy. Or having an NRA sticker says there might be guns under the seat that could be stolen. Or the rental car company sticker when your on vacation. Or the out of state plates when your in a tourist area. So there are a lot of ways to advertise.
I have a truck with a cap on the back and used to have old network cable boxes cut so I could stick them in the cap windows so it looked like I was carrying a load of cable instead of my camping/traveling gear but now people steal wire and cable to sell the copper.