Hi Tom,
It's not my toggle
Interesting that you mention DDR reproduction toggle pieces. Never realized they also produced completely new parts, apart from the barrels and springs.
A German-proofed Mauser Parabellum would indeed have a proof mark on the top of the rear toggle.
Could the piece pictured be a scandinavian produced spare part? Both the Finnish and the Norwegian army were longtime P08 users and might have had spare parts produced?