We have a twist ring type of Victorian bell as illustrated on our Victorian home, however the bell itself is mounted on the door interior with the twist dohickey on the outside. (covered by second and smaller plate)
The front of the plate is recessed to accept screws and the tube is probable swedged to that face.
Its all wrong, the plate needs to be reversed to work.
The plate therefore needs to be screwed to the inside face of the door with the tube extending to the outside.
Having said that, its my opinion that its not related to a bell.
Lastly, the oblong opening has a definite function...?