Have you ever given some thought on why bank-notes have numbers and coins not? Some of the coins in circulation in certain economies are worth much more than numbered notes in other economies. So it cannot just be a cost consideration. I was thinking about this when I read the article about placing a unique digital identification inside a banknote (Read here).A definite need exists to be able to track where money goes and how it is being used. (Not that I think that a unique number for each bank-note really does this). Electronic payments, though, do have the ability to make every payment unique. Rather than investing into making bank-notes more "trackable" should one not invest in electronic payment systems?