I had some electrical work done at my house yesterday. When I was writing the check out to pay my electrician he slapped a magnetized version of his business card on my fridge. When I complimented him on the idea, he told me that he kept a bunch stuck to the back of his van below the painted words “Please Take One.” I think this is brilliant! What a great way to use the assets you have! And, yes, he has gotten business this way.
It certainly doesn’t hurt that the back and sides of his van provide additional information like “fully licensed and bonded,” either. 
In this digital age, it is great to see smart marketing or guerrilla marketing that does not require a computer for someone to engage with your business. I love how low-tech tactics can be a smart differentiator!
Love that idea, especially the take-away aspect, when the truck is parked at the curb. Also would argue that you don’t forget about the real estate on the TOP of your vehicle – anyone in an office above the 3rd story can see that space, and putting your logo/# or product visual on the TOP of your truck is an easy, cheap way to spread your name. As I sit on a lengthy conference call, gazing out of my window, what else am I going to look at?
Sam – That’s a great point re the top of the vehicle!