1- Only do this in parking spots and set up road cones for added safety. Might want to have a friend standing by too wearing one of those reflective vests.
2- When a suitable grease stain is found, using chalk, draw what the stain inspires, transform it into something beautiful. Maybe that splotch
can be turned into a swan with the Moon behind it, this other splat can be turned into a mythical beast with 8 arms.
Hmm, now that I think of it, this might be a cool thing to do in art class. The teacher comes around to the canvases and throws a handful of paint, only slightly darker than the canvas. The students then take this random splotch and make a work of art out of it.
I can see it now, "Hey, that guy got a masterpiece splotch and mine sucks!"
To which I'll add, psychiatrists could use this too and an extension of the Rorschach test. They don't tell you what the ink blot looks like, they show you. One person might draw a happy kitten eating jelly beans while another might draw an apocalyptic scene of devil rabbits eating New York from the same splotch.
The more relaxed atmosphere of quietly drawing might lead to more openness than being grilled by the guy with the pointy beard and creepy German accent.