is what is used to remove faux frosted or etched film from window glass.
Be advised if this contact(brand) like vinyl sheeting was applied to historic glass it is very easy to scratch/etch accidentally!
Oftentimes it is wisest to first remove the sash itself prior to beginning work.
If the window glazing (glass) has any significant age to it - and it doesn't have a safety glass or tempered indication (found in one of the four corners of the exposed glass) it would be wisest to take the removing of the sash first before working precaution.
Also if this is a single glazed sash(just one layer of glass in the sash) be very careful applying pressure against the glass itself if you choose to work in-place - as the glazing compound/window putty might be brittle and the metal points holding the glass in place can handle very little pressure against them before they might bend (points are little pieces of cut thin metal which are pushed into the sash (if wood) and extend onto the glass underneath the glazing compound/window putty.
Avoid using a metal tool or razor blade to scrape the adhesive or lift the film - as you may leave visible or fine scratches in the glass.
If alcohol doesn't remove the sticky glue try a household ammonia solution or ammonia containing window cleaner. If it still doesn't budge - try orange oil or lemon oil.
Also note: some films are static charged and don't use adhesive or glue at all, usually teasing off the corner is the most difficult part of the process, sometimes helped along with a dental pick or a tooth pick and a wet sponge (with either hot or cold water - which ever is the opposite temperature of the surface glass at the time you are working) on the corner.