Use a metal scraper or knife to carefully scrape off as much of the silicone as you can. Go very gently and carefully; if you move to fast or cut in too much, you will scratch the surface of the window. Wedge the edge of the scraper under the silicone and then lift up as much of it as you can with the surface of the scraper.
Brush off any loose silicone once you have gotten off as much as you can with the scraper.
Use a kitchen scouring pad to buff off more of the silicone. Dampen the scouring pad slightly, then use gentle circular motions to rub the remaining silicone.
Brush off any loose silicone once you have gotten off as much as you can with the scouring pad.
Use a product such as Goo Gone (see Resources) on the remaining silicone smear. Apply according to the directions on the bottle, then wipe off as directed.
Repeat applying and wiping off the cleaning product until the silicone is gone. You may need to go through the process several times.
Clean the window with a normal window cleaner and a squeegee to remove any remaining streaks.