Small Cup 2S 90 marking

[Silversmitty]

I recently purchased this item with a small collection of different silverplate from Oneida, Alvin, Gorham. I have no information as to the age, etc.

The marking looks like 2S 90
It is aprox 1.75" tall by 2.5" outside top diameter.

If anyone is familiar with this type hallmark or this type of dish and what it is I would be very grateful!

I am not certain this is plate versus 90% silver either so that information would also help.

Thank you!