According to nospambob :
Acetone is another powerful solvent that I'd try.

Might want to experiment with some gelled paint stripper. That'll
remove just about anything and _should_ be safe on glass. Test
first to make sure it doesn't etch the glass even more.

Used the gell variety, so it doesn't just flow off the window.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.