text: Although the portraits and legends changed with the political changes in France, the denomination remained in usage until World War I under what was known as the Latin Monetary Union, the "Euro before the Euro", so-to-speak. Switzerland had 20 Swiss franc pieces, Spain had 20 peseta coins, Italy had 20 lira pieces, Belgium had 20 Belgian franc coins, and Greece had 20 drachma coins, all of which circulated and were accepted throughout Europe. Only for political reasons did the United Kingdom and the German Empire refuse to follow this direction. Attempts were even taken to explore the unification of the European currency with the American dollar, which explains the extremely rare U.S. pattern coins carrying $4 marking on the face and 25 franc markings on the reverse.
  Distinguishing marks of the mint masters
  The coins bear the signature of the master engraver responsible for the engraving of the coins' dies. In later times the engraver used a symbol to identify himself. The coins also bear the mark (a symbol, letter, or monogram) denoting the particular French (or French controlled) mint which struck the coin. These mint marks often signal the rarity of the issue, for example the Napoleon 20 franc gold coin struck in 1809 at Paris and marked with the letter "A" had an issue of 687,508 coins; in the same year at the mint at Bordeaux, marked with the letter "K" only 2,534 coins were struck; while the mint at Lille, marked with a "W" struck 16,911 coins. Over the years there were some twenty-three French mints not only in France but also in annexed or occupied countries, including Italy, Switzerland and the Netherlands.