For those who don't know, semacodes are kind of two-dimensional barcodes. Little black and white grids of squares that are used to encode text, generally a URL.

In Europe and Japan they are often used for advertising, among other things. An ad will contain a small semacode in one corner that resolves to a URL. There are free java apps for most phones that will use the camera to take a photo of the semacode and then open the URL in the phone's browser.

Some high flying types even have them on their business cards, pointing to their web site or something.

More information over at wiki: (this is the one used in Japan, it has squares in the corners as position markers)