Offered for your perusal are three examples of the same styled knife, though each was manufactured by a different company. The top knife is from the firm of Union Messer-und Metallwaren Fabrik Zella. The middle one is from the firm of Hugo Koller and the bottom knife is unmarked and its maker remains unknown. This style of knife is most commonly associated with the firm of Union Messer commonly and erroneously referred to as “Union Zella” because of the blade’s markings. Of the three knives pictured, the Union Messer’s variant seems to be the most commonly encountered.
Only the Hugo Koller variant has a “fraktur” acceptance stamp of the letter “C” marked upon the (opposite from the manufacture’s logo side) ricasso. This indicates a government sanctioned inspector had deemed the knife satisfied a minimal level of quality to be utilized by a Soldier/Sailor of the Imperial German armed forces. The implication being, a knife with a “”fraktur” mark was something that was cleared to be purchased by the government for issue hence the inspection. If there’s no “fraktur” mark present, it’s generally assumed the weapon was a privately purchased item offered for sale to the Soldier/Sailor and purchased with their personal funds. Trench Knives and various knife bayonets were offered for sale at the Soldiers’/Sailors’ canteens, from traveling salesmen/outfitters, at various specialty stores, and through direct mail order.
These three knives may be viewed in Halasz, H. v. (1996). Deutsche Kampfmesser: Band I. Norderstedt: Militar-Verlag Klaus D. Patzwall. The Hugo Koller variant is shown on p. 67, the Union Messer on p. 68 and the unmarked variant on p. 69. The Union Messer variant is also shown in Méry, Christian. German combat knives: 1914-1945. Paris: Histoire & Collections, 2011, on p. 42. The two pictured German Soldiers wearing similar styled knives are also from p. 42 of Méry’s outstanding book. Fellow forum member, “Reibert” has posted a very nice postcard of a WWI German Soldier with one of these styled knives found in the very first post of his thread here Postcard of a German Soldier with trench knife