Portal got some weird achievement and update, and it is the most cryptic thing I've ever seen Valve do. Probably something for Portal 2 or an expansion, but jeez laweese. D:
Apparently, it's a sound that you listen play on the radio, and it sounds all weird and jumbled. Then, if you figure out that the jumbled sounds are actually images, you put it in a program, and find the weird cryptic message made through the sound files.
http://forums.lambdascience.com/showthread.php?tid=77
Out pops those.
How the hell, were you supposed to know to listen to a radio message, and instantly think "Oh yeah! That's an image! Let's see what it is!"