Salt on a driveway that was probably picked up off the road in the tires and mixed in with slush then melted off and dried into neat patterns as the water evaporated.
I used the digital mirroring here again, the same photo duplicated 4 times and rotated to line up with the others. I first noticed the portal like hole in the middle. Then to my surprise I saw twin mouse men with raised arms "guarding the portal" I had to ask my brother what he saw just to find out if he saw them two and he did, but that doesn't mean I'm not crazy. ;-)