[shorod]

What are the chances there used to be window tint on the window and what you are seeing is just the tint adhesive that did not get cleaned off? You may test this theory by using a rag you don't much care about along with some lighter fluid/isopropyl alcohol/acetone/laquer thinner/brake cleaner/throttle body cleaner to see if you can clean a spot off. Start in an area where the defroster and antenna lines don't exist. However, I've used just about all of the above (one at a time) and none have attacked the orginal defroster grids.

Or, you may want to try a razor blade on a flat area without the grids to see if that cuts through whatever is on the window. Razor blades will however quickly destroy the defroster and antenna grids.

-Rod