You might have seen QR codes around. These quick response codes provide those who have special readers on the camera-equipped mobile phones to scan the image and go to content (usually a website) that has been linked up with the code. You can actually create these codes for free using sites like this one. You can even download a free reader here.
If you want to learn more about this tool, click here for an article about how non-profit organizations are making use of it.