Submitted by Neal:
You'll have to click on this one for the full size.
It's a pull from Douglas Adams' Hitchhiker's Guide to the Galaxy. The number 42 is obvious for anyone who has read the book as being the answer to life, the universe and everything. The "don't panic" on either side of the number 42 is also from the book, wherein Douglas Adam's claims on the front of the actual Hitchhikers Guide (the one in the book not the book itself) it reads "Don't Panic" in very friendly letters.