It's too bad there isn't some sort of reconfigurable QR code stamp thing that you can use to sign something. Say, for example, you enter in the payee, amount and date, it digitally signs it with your private key from your bank, creates a QR code with the data and moves tiny little stamp pins up/down and you press it onto the paper.
Other than a bank or cheque cashing service, anyway...
The niche seems pretty small: payments too large for cash, too small for certified bank drafts, to people taking too few payments to have technologying up make sense.
