The only place we were really told to tone it down - where other people would use the word censorship, but I wouldn't - was when we did MTV right after the Beavis and Butt-head thing.

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.