Welcome to the forums from the cotton and peanut covered plains of the Wiregrass! Your M13-2 was made in 1981. It was exported to the UK as indicated by the Birmingham Nitro Proof stamps on the cylinder. There should be an importers stamp, perhaps on the flat area under the barrel where the extractor rod docks. It may be small. You can request an Historian's letter of authenticity from the S&W Historical Foundation, but I doubt it will tell you anything but an exporter agency as the destination.