The harp-looking logo on the guard is the Tokyo Suya logo; The "harp" is an artistic version of the first kanji in their name: 壽
壽屋商店
Suya Shōten
See JapanX's informative site here.
-- Guy
For an in-depth article on Suya Shoten, see Nick's piece here: The Untold Story of Suya Shoten
Ohmua's site has some history of the dirk, with examples of several versions here: Naval-Dirks
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