Paint overspray on a car window looks plain sloppy--kind of like a coffee stain down the front of your shirt. But it's something you tend to ignore because you think it's a hassle to remove. Actually, it's very easy to get off light overspray, and with a little elbow grease, you can get off a heavier coat. You end up with a fresh, clean look that makes you wonder why you didn't tackle the problem earlier.
Pour solvent onto a soft rag. You can use acetone, paint or lacquer thinner, white spirit or MEK (methyl ethyl ketonon)--they're all available at paint and building supply stores. Use just enough solvent to wet the rag, but don't make it dripping wet because spills can harm the paint on your car. Wipe the window with the wet rag, and the light coat of overspray should come off.
Use a retractable safety scraper or a razor blade in a plastic holder to remove a thicker overspray. Scrape the paint off the window carefully, and vacuum or wipe off the paint shavings. Apply a coat of solvent (as in Step 1) to take care of any places you miss with the razor blade.
After Step 1 or 2, apply the acetone or other solvent again. This will thoroughly clean off the window and eliminate streaking. Wipe with a fresh cloth. Wash the car with soapy, warm water. Dry the window.
Use solvents such as acetone in a well-ventilated area, and be careful not to breathe it in.