In my experience, they're now yours permanently. I tried using a very, very soft sponge (like for washing infants) and it left the swirl marks. So now that side has stickers on it and the other side is still spotted.
We got similar, though not identical, spots after the following: we drove on a road that was graveled with crushed calcium carbonate (the roads look like gravel roads, but appear very light, almost white.) The rig was very dusty and we got rained on. Got home and noticed the spots, so went...
We were driving on gravel roads that are covered with crushed calcium carbonate instead of gravel, which isn't uncommon in areas of north central washington. On the way home, we stopped and had the Bronco washed. The areas where the calcium dust (it's white) had collected in the rim around the...