Remember QR Codes? They’re More Powerful Than You Think
I like the functionality of QR codes, but the fact that they're not human readeable makes them unsafe. It would'nt be unthinkable to make a QR-code, paste it over an existing one (for instance: the QR code in the bar to pay for a tip) and redirect the user to a spoof website where they can tip me instead of the bar/musician.