Quick Response Codes are popping up everywhere – those little black & white squares you're beginning to see in magazine ads, conference badges, even at national parks. Though they're sometimes likened to UPC barcodes, they're much more powerful and have become one of the hottest mobile applications in the marketing world today.

QR codes are two-dimensional, matrix barcodes that can hold unique data for websites, personal URLs (PURLs), virtual contact cards, phone numbers or instructions for mobile device users to follow. Initially used for inventory control, QR codes are now available to anyone with a smartphone and free reader app. And with this mobile technology quickly gaining popularity, it's no wonder marketers are looking for ways to use this technology to reach their customers.

A quick scan of a code on a direct-mail piece or email can take anyone with a smartphone to online content without typing a web address. We've seen some innovative uses, such as advertising a new shopping center, in which a user scans the QR code and is taken to a microsite with mobile coupons for mall shops. QR Codes are also making their way to conference badges as a substitute for handing out business cards. You can find them at historical landmarks, where codes guide users to the next location. And you can even find them on tee-shirts with codes pointing to a Twitter feed.