I googled what you asked for and here are some URLs to check out.

Here is a link that might be useful: Removing film

Here's a photo of what I'm talking about. I guess it's not really baked on - it's more like mineral deposits, although these are 2nd story windows and sprinklers would never reach them. I even tried Limeaway and it helped only a bit but did not remove it. I'm at a loss. Anyone?

Call a company that installs film and see what they have to say. In some circumstances they may have to remove the old to put on new.

Are they double pane windows? It sort of looks like the seal (between the panes) might be broken in the top one.

Is there a problem with both the upper and lower windows?

I thought it looked like damage from water on the inside. I had that happen to a patio door one time.

Yes, it's a deposit on the outside. I can feel it on there. The lower half has it too but not as bad. I don't think it's a broken seal but I'll check it out again this weekend to be sure. Will give the cleaner suggestions a try, maybe use a razor blade. Thanks for the input!

I have the same problem. The sprinkler hits the windows and we have lots of minerals in the water. I tried the toilet bowl cleaner and it worked! Thank you for the suggestion.