The Ace 250 found this for me at a site that has yielded a lot of 1920 era relics. I can't make out the entire backmark, but based on info from another website, it was produced at the Conduit St. address of this company (http://www.ukdfd.co.uk/pages/buttonsntoz.html). That narrows down the date range to 1856-1918. If there are any button experts out there, additional information is appreciated. - ziphius