Lol, I wondered if anyone would notice
It is an experimental rear sight developed by Mauser engineer and quality assurance guy Otto Repa. He developed the sight (and accompanying modifications to the rear toggle piece) in order to see whether it was possible to create a 2-piece sports sight.
The idea was quite good, the rear sight is held in place by the toggle pin, through 2 cut-outs in the rear toggle part. The problem is that the rear toggle has to be machined to very exact specification, otherwise the sight will bounce up on recoil. This is why Mauser eventually chose to create a completely new rear toggle part for their Parabellum Sports pistols.