A missing serial number is no proof of a counterfeit: only newer writing instruments bear a serial number; pieces from the 1980s and earlier have none, and some more recent special models (early Scenium, Rouge-et-Noir, Noir-et-Noir) too come without a serial number. A practical authenticity feature on Meisterstücks made of precious resin: when shining through the barrel or cap with a halogen spot, a reddish shimmer becomes visible. Detailed identifying features together with picture comparisons can be found on the fakes page of fountainpen.de; in case of doubt, an expert assessment based on meaningful photos is advisable.