You don’t have to be brave or a saint, a martyr, or even very smart to be an atheist. All you have to be able to say is “I don’t know”.

It has been featured in dozens of television shows and articles and was designed by his friend Colin Summers. From a FAQ from Penn & Teller's official website there are three common answers:
It means he once shot a man for asking personal questions. Drell

Babylon 5
"Day of the Dead" (1998) TV episode.

Penn Fraser Jillette (born March 5 1955) is an American illusionist comedian musician and best-selling author known for his work with fellow magician Teller in the team Penn & Teller.