Did you ever see that sand art this Japanese guy did on top of one of those presentation machines? You know, the ones where you put clear plastic sheets with writing on them on it and it projects the image from the sheet onto a wall?
This guy covered on of those projection machines with sand and drew with the sand and with his fingers.... it was really amazing watching how he made one picture turn into another.
in my days we wrote "TANKS ARE NOT AFRAID OF DIRT!" (in Russian of course). these vans are commonly used as shuttle taxis in Russian towns and cities, and the composition depicts a traditional Russian wooden church (built without a single nail!).