hi, stickers, try first just wetting and wait to soak,then try a scraper,dont try solvent first as this can make it worse. DO clean the window first as loose grit is what scratches ,then wet again and scrape but be very careful ,if you hear a scratching noise stop,clean scraper and re wet. The worst thing is mastic/silicon, this stuff brings you to tears.It is by its design meant to stay flexible ,scrapers tend to go over new/soft mastic and just smear it into a thin mess. Turps etc dosent work very well ,go to machine mart and get mastic/silicon remover ,i only discovered this after a 13 storey job ,it works.Finally treble what you think! good luck mate.