Spanish coin, cup???

I’ve had this ‘cup’ for several years and have no clue what it’s purpose or maker is. Have enjoyed researching both questions, but need help!! Base is made using a 1777 milled Spain silver coin. Maker’s mark just under the lip of the ‘cup’ is the letter ‘M’ over the letter ‘G’. Any clues I seem to be missing or answers to “What Is It!” would be greatly appreciated! Many thanks, in advance!

Here are some other images of my ‘cup’.

As to ‘what’ it is, I would think the item is a TASTEVIN, which is a is a small, shallow silver cup or saucer traditionally used by winemakers and sommeliers when judging the maturity and taste of a wine.
I think the mark you show is a Spanish silver maker’s mark (usually accompanied by a pentagram mark which would indicate the silver quality of .915). Others may help further here.
Best regards