I can't identify the maker, but the hallmark style seems consistent with "Chinese Export Silver" and my best guess would be that this is some kind of gaming counter used for a game of some kind, or perhaps used as a way to weigh down a piece of paper during a game of chance, that's the best I could come up with :::
I think the first place to look would be in the category of "Chinese Export Silver" and try to figure out who "Y.T.K." would be :::