My car developed  small round blurs in the middle of the front windshield – visible and annoying only when the sun angle was low.  After being puzzled for a while I remembered that I’d driven up to Dallas and met my friend Kristin at DFW and after we navigated through Dallas and returned to Houston, she borrowed my car to go around town;  and she has a portable GPS.   And it has a little suction cup to attach its antenna to the windshield.  Aha.  This was like when you  park your car and come back to see by the paw prints that a cat has strolled up the windshield, except these were in the inside:  GPS paw prints.