Many pizza places, including the one I drive for, require drivers to have "Car Toppers." These are big plastic advertising signs that attach by big magnets to the top of your car.
Many drivers don't like to use them at night, especially in bad neighborhoods. They worry that the car topper is an invitation to hoodlums that the person is carrying money (and food) and would make a good robbery target. I stay aware enough of my surroundings that this has never been an issue for me.
Some drivers with nicer cars also don't like to use them for fear of scratching their car. My cars have always been old enough that I don't really worry about it.
Well today in downtown Cleveland, at the end of my daily run, I saw a pizza delivery car for Cleveland Pizza & Calzone Co. with a unique idea for saving his car from scratches. He had the topper on his trunk, but under the topper was a dishtowel. The magnets are strong enough to work even through this small layer of cloth, and the towel was protecting his car from scratches.
I though this was an interesting idea and am surprised I've never heard of it from another driver.