3.14159 are the first five digis of pi. The signature follows the title, basically. I had seen Ren with his pi avatar and found it to be good - so when he changed, I asked him if I could use it. He said sure, just give me some recognition. I added the third line to my sig and put an "R" in the pi avatar.
The fourth line was added in a thread asking what your avatar meant. Insurgent posted a better drawn pi avatar - so I used it and linked to that post, the fourth line.