Crop Circles

So I don't really know what to make of this. I do know it is one of the coolest pieces of graffitti I have seen in San Francisco. I ride my bike by it a couple of times a week. It seems to be made out of tin foil pressed onto the pavement. This is a method I have never seen before.

There is a small signature also in tin foil nearby, it is just a little tin S.

Location: Taylor and California, across from the cathedral