If you’ve tried to photocopy banknotes since about 1996, you may have found that your copier won’t cooperate — many machines will balk if they detect a pattern of symbols like the one on the left. Eight such patterns are marked on the U.S. $20 bill at right.

The authorities have been understandably mum about the details, but the pattern has been discovered on more than 30 world currencies. It’s known as the EURion constellation.