This is called a QR Code (short for Quick Response Code, aka a two-dimensional code), which is a registered trademark of DENSO WAVE INCORPORATED. Basically, it's a better bar code that's moved outside the supermarket and into consumer advertising. Why is it better? It has the capacity to contain much more data (up to 4000 characters) than a standard UPC code and has faster readability.
Smartphone users can install a scanner app that reads the code and converts it to a URL or other data, like e-mail addresses, SMS text, vCards, plain text, and more. Upon scanning, the code directs the phone's browser to the desired website, data, e-mail address, etc. And yes, it's free (and easy) to make your own 'mystery box.' There are a plethora of websites where you can generate a QR Code for free. I've listed a few below that I've played around with and seem to work well, but this is by no means a comprehensive list:
But why? you ask. What's the point? Well, the QR Code is another easy method of reaching potential customers (aka readers) and giving them a new way to discover your website (or your book's website, or your blog, or wherever you'd like to direct traffic). Will it sell more books or garner you a larger fan base? Maybe, maybe not. But it certainly won't hurt, and you won't spend a lot of time making your own QR Codes--it only takes minutes (or less if you type faster than I do).
What does my QR Code do? Scan it and find out!
Since I've already included a picture in this blog, I'll just leave you with a link to my Pinterest page, where you can peruse cool images that remind me of Crimson & Cream.