Japanese tea set

I have this set of 4 tea cups and saucers from my grandmother house. No one in the family knows anything about them. I am especially interested in the mark on the back of the saucer. (tea cups have no marking) I have looked through many web pages and haven't been able to find this mark. I'd appreciate any information. I would like to pass them down to my daughter and would like to be able to tell her there history. Thanks for your help!