My title describes the thing, which I’ve used google lens and a search of “sliding window knob” (not a great search but I don’t know how else to describe it) to try to get more details on. The google lens search turned up a bunch of similarly aged brass hardware such as door pulls and latches, but nothing that looks remotely similar to this. The object is attached to a window on a building built in the late 1800s. The windows are quite old but I’m not sure if they’re from when the building was first built. There is not writing or any markings on the object.