Today in my ongoing series of photos from my travels over the years: a sign in a cafe in the Vienna airport declaring the 500 Euro note invalid. This is the most valuable note in the world I’m wrong — there are Swiss and Latvian notes that are more valuable — learn something new every day! — part of the answer to the logistical question of transporting lots of black-market money around, and it’s natural that it would end up a counterfeiter’s dream. There was talk of embedding anti-counterfeiting RFIDs in the bills, but I can’t tell if that ever went through — certainly, it seems like a genuinely bad idea to make it possible to remotely detect which wallets are worth stealing. The sign was laminated (hence the poor quality of the photo), and it made me wonder about the secret life of the world’s most valuable note.