50 Mark - 2018 "Willy Brandt"

This is not an official Bundesbank issue. The Federal Republic of Germany has issued no paper Mark currency since the euro changeover in 2002, and the Mark was never reintroduced. Notes of this type — commemorative or novelty items bearing post-euro German denominations — are produced outside the central banking system and carry no legal tender status. The "Willy Brandt" attribution places it within a wave of German commemorative paper produced for the collector and souvenir market, not monetary circulation.

A watermark in a non-monetary item is a production choice, not a security measure in any meaningful regulatory sense.