Secret Service's special code names for Mitt Romney and Rick Santorum

Related: Secret Service code names for U.S. Presidents & their spouses

The top three GOP presidential candidates have Secret Service details assigned to protect them (sorry, Ron Paul). Last week, GQ magazine revealed the code names Mitt Romney and Rick Santorum have chosen for their protector agents to use when referring to the candidates.

"According to multiple campaign sources, Mitt Romney elected to call himself 'Javelin.' And Rick Santorum chose 'Petrus.' The use of code words to refer to candidates are a throwback to the era when Secret Service and White House Communications Agency communications were not encrypted. The tradition has stuck around. The only real rule the service has is that the word chosen be comprehensible over the radio and not be similar to someone else's. That's why code names tend to have two or three strong syllables."

Romney's code name is widely believed to be a nod to the Javelin muscle car produced from 1967-75 by American Motors Corp. — the same Detroit-based company Romney's father, George, ran for eight years.

The Secret Service nickname for Santorum is a nod to the immigrant grandfather the candidate often references during campaign speeches. In an appearance on Fox News last week, Santorum explained his choice of "Petrus" — and also took a swipe at Romney's "Javelin" handle.

"You've heard me talk repeatedly about my grandfather. His name was Pietro. And I just didn't think Pietro would work. I just — it's a name and I didn't want a name. So I thought Petrus, which is the Latin word for 'Peter' and for 'rock.' I thought (it) was a more apt name than an Italian name for Peter. … I remember the Javelin. It was a very — it was an unusual car. So I think it sort of fits."

Related: Secret Service code names for U.S. Presidents & their spouses