It is a Montblanc Safety from the 1920s in size '0' — the second-smallest build of the time (smaller was only the '00'/Baby model). The model size is engraved on the nib. Such Safeties were at the time often individualised with precious-metal overlays by goldsmiths or jewellers; the overlay therefore typically does not come from Montblanc itself. For value determination, comparison with currently running eBay auctions of similar pieces is recommended, since collector prices depend strongly on preservation state and overlay quality. The regular eBay marketplace (not Kleinanzeigen) offers international reach for achieving market-appropriate prices.