sandwich board 
noun
A pair of advertisement boards connected by straps by which they are hung over a person’s shoulders.On Orcas Island, my wife and I noticed a sandwich board advertising half-day sea kayak expeditions, ‘No Experience Necessary.’...
- If I see you wearing a foam trucker hat, then you might as well be wearing a sandwich board advertising a cheap Chlamydia remedy, because I'm going to walk on by.
- We dodged past a camel walking by with a sandwich board advertising Cut-Price Jeans on either side of his hump.