Featured Gorham Sterling Cup - Decode Mark Help

I have hopes for this sterling silver cup with a gold wash interior, but for the life of me I can't figure out the nuances in the Gorham marks. Am pleading for help here. Spent hours looking at my mark and the examples. They mostly look same to me.
I suppose it is a monogrammed baby cup, as it is only 2 1/2 inches tall and 2 1/2 inches in diameter not including the handle. But it is a whooping 93 grams of sterling, so it might be too heavy for a baby and was used for something else. Until I figure out its use, I won't be able to find out anything on my own.
I tried to polish it, but some of the stains are not coming out and I don't know why. Is there a silver disease of some kind or am I not using enough elbow grease? Please any help appreciated.

 

This link fits in with the period of time without date symbols ...
https://www.worthpoint.com/worthopedia/gorham-sterling-51-baby-mug-3777578157

another link with the same style ...
https://www.replacements.com/silver...ing-hollowware-gold-lined-baby-cup/p/25269531

 

That first one seems to have the same mark "51" but it's hard to tell. I would be happy with 1939. Thanks for tracking these down. You seemed to have answered the question as to is it a baby cup. I have a Lunt baby cup and it isn't nearly as heavy.

 

The text in the worthpoint link also identifies the number as 51.

 

You're right. I missed that. I think it is a product number. I'll do some searching on that. Thank you.

 

I vote for baby cup. Silver or silverplate baby cups were generally decorative/commemorative items and not actually intended for use. Nice find!

 

Aha. I thought it was for rich children who threw their cups