I'm reading Goldblatt's "Topoi: A Categorial Analysis of Logic."
There's a symbol I don't recognise on page 302 of the copy with International Standard Book Number 0-486-45026-0. It's in the definition of a natural number object and resembles a cross between $s$ and $\sigma$.
For lack of a better format to show you what it is, here is a picture:
I have tried using Detexify but to no avail.
What symbol is it?
Please help :)