Now what does that mean exactly? I have seen it engraved on the ribs of shotguns not made by H&H.
I'm looking at a reprint of H&Hs 1900 catalogue and you can have your Webley .455 MkIV 4" revolver shot and regulated as well as your Colt New Army Pattern also in .455, but they do not offer this service for the Colt Bisley Model in 455 or 450, I do not know whose .450 that is, might be the Mk 1 .450 offered for the Webley Green (WG) Army revolver. No semi auto pistols offered in this catalogue except the mighty Webley Fosbery "Automatic Revolver.
Mike