Wickd (site moved to W-41.com) are selling a range of T-shirts with a ShotCode logo on the back. The proprietary two dimensional barcode is unique for every product and is linked to the user. You can link your code to any url such as your own mobile site, your MySpace or Facebook homepage etc. If you use your Wickd profile you can even exchange private messages. The only negative is that ShotCode, unlike QR code, is not open source and is not so widely used internationally.