Each of the semiconductors in our computers, cell phones, microwaves, etc. is produced by layering semi-conducting silicon and aluminum. The circuits in these chips are meticulously designed, and once in a while a designer will hide a bit of his/her own artwork in the circuit.
These little images and drawings aren't very deep. Chip people aren't typically creative types, and there's not much you can do in this medium. What's special about these signature designs is that they were never meant to be seen. Apparently they are discouraged by the companies that produce the chips. They can only be found if you pore over the actual circuit with a microscope.
Chipworks is a company that does exactly that. They don't do it to find the art - they have other reasons. But they have put up a gallery of the images that they've found. These are little ghosts in the machine, cave drawings for future techno-archeologists.
http://www.chipworks.com/art/silicon_art.htm