In the sunlight or from a distance, you can see a rainbow stain along the windshield, it's quite big. What is that? How can i get rid of it?

I bought this product called, "D'Best Windshield Polishing", i rubbed it in, washed it off, it didn't work. I then tried vinegar with water to no prevail, then I tried a little bit of acetone, still didn't work. Is there a product that I could buy for a DIY at home? how much? I'd rather not take my car to a shop to get that fixed, magastos heheh. I'd rather do it myself at home. I have no tint on my front windshield,except for the top 1/4 portion of the windshield, there's a strip of tint that I decided not to peel off when I removed my tint up front. I have a 92 Sentra, 2nd hand, not sure what the 1st owner did to it or how it got that way. Any ideas??