Comet and some elbow grease will really a number on the window. Be sure to use as little water as possible to insure maximum grittyness
NOT 
Years ago, my grandmother called me and whispered into the phone, "Randall, I need you to come over and see the mess I've made to your grandfather's car."
I said, "What's wrong with it?"
"Well" she said, "I went under a bridge and they were pouring concrete and it put tiny drops all over the hood, roof and trunk of the car. I tried everything to get it off before your grandfather came out and saw it, but nothing worked until I used the brillo pad."
________________________ <-- this is my reply. Yes, for once in my life I was speechless. However, I was thinking "OH ****************!"
As she started to cry, she said, "The car looks worse than ever now. I scratched the paint here and there and I need you to come over and see if you can buff it out."
Gentlemen, I had never seen such a nice paint job on a 1 year old car look so bad. It looked like a dozen cats with 50 claws on each paw tore into that paint job all over the place. She scrubbed on that paint job for at least two hours with what I saw.
Thank God my grandfather couldn't drive any longer and didn't have to look at her work day after day. Sadly, I could not clean it up much... but I did use a light rubbing compound and a good wax and it really reduced it from what she saw when drying the car off after the brillo pad scrubbing.
:ah: