Decorative window sash

[fov]

In San Francisco those corbel things are called "ogee lugs" and most of the early 1900s era homes have them, or did originally. If your windows are visible from the street, SF has strict rules about what you can do with them and if you have ogees you are required to keep them. The rules aren't always followed but you still see them all over the place here, they're considered a defining period detail of the house.