HI! welcome to Kaizen and Kakushin blog site here we will help you to clean that windshield of yours :)
Terms:
A watermark is an identifying image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, atop a dark background), caused by thickness or density variations in the paper (ref. https://www.google.com.ph/#q=watermarks)