I think it's Adobe Photoshop. I have it on one of my computers (with very bad RAM so it freezes occasionally), and I think that's one of the effects you can add.
-¤MaynardsTOOL¤- are you a professional? How did you do the box thing on your sig?
A lot of people think I'm pro (which I hope to one day be after the next 4yrs of college -.-), but I'm not. I'm only 18, so I haven't been able to make a name for myself beyond my website (click my sig), and www.rocktoons.com . Thanks for the compliment though. I make all of my sigs with Photoshop- the one I have now consists of many different effects. To achieve the blocky effect, I created a pattern (of 8px x 8px) blocks, and put it over the other layers, then subtracted away some of the squares. :P