If you don't know what QR code or if you've seen these around but don't know what they were called, here is a good description from wiki:
A QR code (abbreviated from Quick Response code) is a specific matrix barcode (or two-dimensional code) that is readable by dedicated QR barcode readers and camera telephones. ... The information encoded may be text, URL, or other data.
Here's how to generate a QR code:
- Open your web browser and navigate to your favorite QR code generating website. This free QR code generating site from Kerem Erkan came highly recommended. The better sites will allow you to create the file in vector .eps format—definitely preferred!
- Select a Code Action which will most likely be "Browse to a Website" but there's a whole drop down menu of options.
- Select Code Type: QR Code
- Select Output Type: Encapsulated Postscript (EPS) (vector data is preferred because it's crisp at any size)
- I left the defaults for the rest. URL Shortening: None, Error Correction Level: Low, Block Size in Pixels: 10, Margin Size in Blocks: 1, Foreground Color: #000000, Background Color: #FFFFFF, Transparent boxes unchecked
- Click the Generate Code button and the file will automatically begin downloading
- Insert the code into your Photoshop, InDesign or Illustrator document. QR codes will be hard to read at sizes smaller than .59 inches (15 mm). A good standard QR code size is around 1 inch or 25-30 mm.