small silver cup with pearl at bottom

I am only trying to identify this item. It was sent to the states from Japan during WW2 as a gift to my great, great aunt from her nephew. I have several items he also sent her but this one has me stumped. It is stamped SPRF on bottom and is a very small cup/goblet, it is heavy unlike silver and may contain some pewter. I just want to know what it is. At bottom of cup is a pearl. I am only looking to identify it, any help would be greatly appreciated!!! Thank you, Cristy Fisher