I would greatly appreciate your help please with this series of hallmarks on a gold pin. The pin has a French eagle mark for 750 / 18K. And a maker's mark, which I believe I have identified as Amédée Datigny, 1892, workshop located at 44 rue Saint-Augustin, Paris.
However, the final hallmark is eluding me. I believe it is a 56 zolotnik Russian mark. But why would a 56 zolotink mark be on an 18K French pin? The gold does test as 18K and not 14K. I wonder why they didn't use the 72 mark? This little pin is an enigma for me.

