Might be a bit tedious, but depending on how much writing we're talking about, Dremel makes a polishing wheel and polishing compound. I've used it to take rust stains out of a glazed ceramic license plate. Works well, but I have no idea what the grit rating on the compound is. It polished the plate to a mirror like surface.

Absolute WORST case scenario is to toss a brick at the windshield, and claim in on yer insurance.

 

I agree with the steel wool suggestion. Just be careful around the edges where the rubber trim is.

Just use invisible glass as a lubricant and rub lightly. Follow with a paper towel or newspaper.