Using code names to refer to political candidates is a remnant of an era where the Secret Service and White House communications channels did not have access to encryption technology.
Harry Truman’s security name was “General” and Dwight Eisenhower’s was “Providence”, J F Kennedy was called "Lancer", suggesting a Camelot theme, and Ronald Reagan, an enthusiastic horseman, was known as “Rawhide”.
More recently, the process of allocating call signs has adopted a ceremonial function, with it sometimes giving the opportunity for figureheads to project their personalities or humour.
“Smurfette” was one of the more unusual code names, chosen by Al Gore’s daughter Karenna, who was 19 when he father became vice president in 1993. Al Gore himself was known as “Sawhorse” before changing the name without giving a reason to “Sundance”.
During George W Bush’s eight-year tenure in the White House he was known as “Trailblazer”, with twins Jenna and Barbara known by aliases “Twinkle” and “Turquoise”. First Lady Laura Bush was known as “Tempo”.
Code names have also sparked unintentional controversy.
In 2007, conspiracy theorists jumped at Barack Obama’s choice of code name "renegade" and its inadvertent association with deserting a religion, especially the name’s Spanish origin – renegado – meaning “Christian turned Muslim”.
Keeping to the tradition of selecting names with matching first letters, First Lady Michelle Obama chose the name Renaissance, and daughters Sasha and Malia assumed “Rosebud” and “Radiance”. Vice President Joe Biden selected “Celtic”.
When the Queen visits America she is known as “Kittyhawk”, Prince Charles is known as “Unicorn” and Pope John Paul II was called “Halo”.
Code names for Princes William and Harry and Kate Middleton have yet to be disclosed.