The only difference between Obama and Bush is that Obama is killing more people. He’s about double the numbers now. Can you imagine if McCain had won and did precisely what Obama has done, with every speech and every political maneuver overseas? There’d be riots in the streets about the people we’re killing. And yet because it’s Obama, and he’s better looking and better at reading the teleprompter, we let him get away with it.

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.