They reveal art underneath.
To promote their newest exhibit, "The Way of the Shovel: Art as Archaeology," the Museum of Contemporary Art Chicago came up with a clever idea - ads that scratch off to reveal artwork underneath.
Printing firm Classic Color helped the Museum get these ads on four bus stops around the city, turning commuters into urban archaeologists themselves. The top coat of the ads flake off when scratched, just like lottery tickets. Printed on back-lit clear plastic, the ads glow even brighter after sundown.