This is a branding iron used at the now defunct St. George Hotel in Dunbar. The George Hotel, recently refurbished as flats, was a coaching inn (where stagecoaches stopped en route for Edinburgh or the south) as well as the collecting point for the mail coaches. Inscribed is 'ST G.S DUNBAR'. 

George Hotel, on Dunbar High Street, was refurbished as flats in the late 2000s, after lying vacant for a decade or more. Once it was one of the largest hotels and hostelries in Dunbar, being also the stop for stagecoaches and mail coaches.