In our example, the code reads X50446027856. The X immediately indicates that the note is German, but a second test is to add the digits. So (5+0+4+4+6+0+2+7+8+5+6) gives 47. Add these digits (4+7) gives 11. Finally add these digits (1+1) gives 2, the code number for Germany. Some countries share a code number.
But while in theory it is possible to identify which country issued the notes, many economists argue this is meaningless and could not be used to split one set of cash from another.
Europe's leaders are at least publicly determined to keep all members inside the euro and as long as they succeed all euros will continue to have the same value.
But in the event of a country falling or being pushed out of the club it will not be long before Europe's shopkeepers and consumers start looking rather more closely at their banknotes.
Land of origin: The code breaker
The 11 digit serial number on every note begins with a prefix which identifies which country issued it.
German notes begin with an X, Greek notes start with a Y, Spain's have a V, France a U, Ireland T, Portugal M and Italy S.
Belgium is Z, Cyprus G, Luxembourg 1, Malta F, Netherlands P, Austria N, Slovenia H, Slovakia E and Finland L.