Do you ever look at the numbers on the euro notes you handle? The significant thing is not the number itself but the letter which precedes it. This indicates the country which issued the note. So Y, M and T indicate Greece, Portugal and Ireland, respectively. Does this matter? Could do. Advises accountancy firm KPMG: “Imagine Greece, say, quits the eurozone. What would be the value of those Greek euros? They could well end up with an unfavourable exchange rate against other euros. Bank accounts in Greece would revert to drachma denomination.” 

So it’s best to avoid those Y notes, if you come across them (and don’t include them in any hoard you have under the mattress); be careful, also, not to hang on to Portuguese and Irish notes. Best of all those with a U (France), X (Germany) or P (Netherlands).