So... this thread got my imagination running...

Not so far future... You get notified that your uncle you didn't even know about died and your presence is required for reading of his will. You soon find out that your uncle was one rich bastard but all he left you was a small diamond. So you decide to see how much the diamond is worth and take it to a specialist. While looking at the diamond the specialist notices there is an engraving on one of the sides of the diamond. Looking closely you realize it must be a QR code. The QR code is your uncles private key for his wallet containing hundreds of thousands of bitcoins. All in a small diamond