Mark ナ on Japanese Orders and Medals: Who and When
As for today the exact owner of this mark remains unknown. Presumably mark was used by Namikawa Yasuyuki /katakana ナ reads Na/. Unfortunately, at present this hypothesis cannot be conclusively proved. Workshop that used this mark was active during the first quarter of the XX century...
asiamedals.info
3rd class Sacred Treasures marked with ナ have two regular marking places: over and under the lower reverse rivet.
Mark ナ over the lower rivet.
Mark.