QR codes were invented by Toyota back in 1994 as a means to easily track products through the manufacturing process. They've evolved somewhat since then, and now come in various sizes and complexities. In short, they're a bar code on steroids because they can represent so much more data in a compact form.
I did some hunting for online apps that would generate a QR code for you from a URL. By far the most flexible one I found was GoQR.Me. They allow you to save the largest version of your QR code, a 1000x1000 PNG image. They also present you with embeddable links if you want to go that route.
Time will tell how well my QR-enabled "for sale" sign works, but it certainly makes life easier for a passer-by who wants to know more about the vehicle in front of them.
Got any other innovative uses for QR codes? Please share them in the comments below!