Here is a very cool short C program. A friend sent this to me. I challenge you to figure out what it does without running it.

#include <stdio.h>

float o=0.075,h=1.5,T,r,O,l,I;int _,L=80,s=3200;main(){for(;s%L||
(h-=o,T= -2),s;4 -(r=O*O)<(l=I*I)|++_==L&&write(1,(--s%L?_<L?--_
%6:6:7)+"123456 \n",1)&&(O=I=l=_=r=0,T+=o/2))O=I*2*O+h,I=l+T-r;}

I have posted the output for those of you too lazy (like me) to compile and run it for yourselves. The output is here.

I've just found a webpage full of obfuscated C programs suitable for inclusion in your .sig.