Provided by a dusty road. Check out the perfectly straight line in the dust along the back edge of the spoiler. (Which I repainted last weekend.) What's weird is the dust shadows left by two round stickers on the glass and a big one on the hatch. The glass and paint look completely clean yet something left behind attracted dust on the glass and repelled it on the paint.
Went from Weiser out to the Galloway dam then roundabout some very back roads to Midvale, then on 95 back to Weiser.