The Solitaire writing instruments with line guilloché changed both their base material and their markings several times over their production life. The early versions of the 1980s carry no hallmark. From 1992 they were made in vermeil, that is in gold-plated sterling silver, and accordingly received the 925 hallmark on barrel and cap. From about 2004 this hallmark disappeared again, because gold-plated brass was once more used as the base material in place of sterling silver.
The hallmark is thus the decisive distinguishing feature: where 925 appears on barrel and cap, the pen is genuine vermeil. Where it is absent, the pen is either an early one from the 1980s or a later version on a brass base — which of the two can only be settled from further features such as the shape of the clip, the engravings and the packaging. The difference in material is reflected in the price as well: collectors report the list price of the early version at the time as around 1,200 DM, and later about 1,800 DM. Before buying it is therefore worth a look at the hallmark, ahead of any negotiation over price.