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
 
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: