To celebrate the 2005 new year, Used COMPANY [遊ずどカンパニー] ran some kind of promotion with UNDER CODE PRODUCTION where this would be given as a gift to those who purchased certain releases (there was one disc for every UNDER CODE band, so I'm assuming the purchaser had to choose one).
The actual contents of the disc aren't known. It's possible that it contained a comment from the band, but it's also possible that the disc held nothing. The disc was printed with a photograph of the band and a small calendar for 2005. It's entirely possible that the calendar was the only function of this disc.