Actually, if you carefully you'll see the s is not an f but a slightly diffferent letter than either. I believe it's called a seriph but feel free to correct me.

I got an answer from me mum:
we used to go by greyfriar's bobby almost every day when we lived at bruntsfield place, but when we lived in oxgangs, we got off the bus there to go to the museum and to the bookshop.
I have a memory of the bookshop being built in a turret kind of thing with a spiral staircase. Any clues?