Posting system specs as a signature is really common on boards where it is more relevant like Travis pointed out. To see it here is kinda weird but hey some people really are into their hardware:)
Well, on forums like @ overclockers.com they put their specs in their sig so you can see what they've got and what they've done to it...
I see no problem with putting your system specs in your sig as long as your compiler name is in there as well.
I'ts not always there to brag....but mostly to let people know what you are runing if they want to compile a program you have(Provided that your compiler name is in you sig)