Home Improvement

Like others have said, I'd give scraping it off with a razor blade a try, glass is actually significantly harder than the steel of the razor so it's difficult or impossible to scratch your glass with the blade. Razors are cheap and readily available (if you don't already have some kicking around) so you have basically nothing to loose by trying it. Also mentioned we're magic erasers/melamine sponges, also a pretty solid bet, they basically work like micro sandpaper.

Failing that, I'm no chemist, but from googling around a bit for siloxane and solvents, I think your best bet for solvents youre likely to find at most hardware stores are mineral spirits, turpentine, and xylene, which should all be readily available in most hardware stores in the paint section with other paint thinners. From what I could find, it kind of looks like you're going to want a non-polar solvent, not a polar solvent like acetone. They may dissolve it outright, or may at least soften it up enough for you to scrub or scrape it off easier.

Also what I gleaned from Google, is that siloxanes are basically silicone, so you may also have luck with products to remove silicone caulk, I know goo gone makes a product for that purpose (although it looks like the main ingredients in that stuff are acetone and benzyl alcohol, which are both polar solvents, so I have no idea how that jives with what I was getting from my other Google searches that suggested non-polar solvents, so again, I'm not a chemist and I'm out of my element)

Any solvents you end up trying, just make sure you're following proper safety precautions, and be careful about anything else you may spray, drip, splash it on, you might ruin finishes, strip paint, damage plastics, etc.