I've made a few sandwich signs. Only highway signs and traffic signals are more interactive. A sandwich sign sits in the middle of pedestrian flow, beckoning people to explore the adjacent establishment.
I designed the graphics and built this sign for C'era Una Volta. It's very heavy, to resist getting blown down. It's very tall, so you can see it. And I really like the graphic I came up with.
It's nearly two years old, has sat out in all kinds of weather, and it still looks good. The value of this sign is something I can't calculate; it's up to the proprietors. I do know that if I average the original expense over the expected lifetime of the sign, it's around 40c per day.
The hardest thing about sandwich signs is that they are not user-friendly. They can never really be heavy enough to withstand wind, nor can they be light enough to be easily moved. It's a system problem without a solution set. When a client asks for one, I work very hard to set their expectations so they will be pleased with the final result.