During my quest to stay current on the latest technology I’ve been doing some research on 2D bar codes, I believe the most common format are QR codes. (check out this handy QR gennrator here). There are tons of applications for QR codes; which are a common way to link physical ‘things’ to their online counterparts. Think of scanning a QR code on a real estate sign (taking a picture with your cell phone) and then being automatically liked to the MLS listing online.
Here is an example of a QR code I gennerated with an imbedded link to my contact page on this website
Random interwebs:

