It's a two-dimensional bar code usually called a QR (Quick Response) code. Created in the early 1990s for inventory tracking, QR codes are now used in B2C and B2B marketing. QR codes store information that can easily be deciphered by open-source software, readily available for all camera/smart phones. Marketers infuse the code with a URL, which sends the user to some compelling content (mobile site or video). Then they place the code in a print ad, an out-of-home ad or a billboard to allow user interaction. If you haven't noticed them on advertisements around the country, you soon will. How does it work? Go to the app store on your smart phone and search for QR Reader. Download a free app and launch it. Point your phone's camera at the QR code above to find the answer to this trivia question:Q. What ubiquitous, medical measuring device was invented in 1862 by Dutchman Hermann Snellen?