If your talking about smearing on the outside of the windows up north, its due to the chemicals they mix in with the road salt.
If I don't wash the salt dust off after a few days, I get a smear it is seen more on the glass than the paint, it is most visible if looking through the windshield into the sun.
If you have problems with inside glass smearing, its caused by the plastics inside of the car giving off gases, leaving this whitish film on the inside of the glass.
Where the weather is hot the plastics give off more gases it leaves a whitish film on the window.
The best thing I can tell you to do with inside glass film is leave a window open a little if you can, it would be a good idea to invest in a set of vent shades.