A maker's mark may or may not be part of a hallmark, and it may appear on a piece of gold as a stand-alone mark in addition to a hallmark. The English were the first to hallmark gold and silver, when they introduced a basic marking system in the 13th century to protect buyers from misrepresented wares. As with the identification and authentication of any precious and fine art items, it takes many years of experience to become proficient in recognising gold makers' marks.
Study the subject of gold maker's marks and hallmarks by reading books such as William Chaffer's "Concise Hallmarks on Gold and Silver." Remember that many makers make gold and silver items and their marks may be the same for both metals.
Visit goldsmiths, jewellery stores, auctions and pawn shops to practice your skills in identifying makers' marks.
Keep a notebook detailing marks as you become familiar with them and to whom they pertain, since you cannot hope to remember them all. French marks, for example, are the most complex of all since they do not consist of any numbers, but instead employ animal symbols.
Research the assay office website for each European country in which you are interested. These contain researchable databases that will provide you valuable information and pictures of maker's marks and hallmarks.
Ask an expert in the field to mentor you as you learn to identify precious metal objects and their makers.
Seek expert advice from at least one expert prior to expending a large amount of money on a European gold item.