I clean bathroom mirrors in public bathrooms and lately several of them have had a cloudy coating over the outside of the glass. The only way to get it off is to use a green scratch pad and scrub gently with glass cleaner till the pad starts to slide smoothly across the glass, then dry with paper towels. There's a reddish orange residue that is coming off which looks like rust. There is no smoking in the building of course so smoke residue was ruled out.
By Lori J.