The royal family may have to follow endless rules and regulations about what they can't eat and how they must descend stairs, but when it comes to giving each other fun and ridiculous nicknames they lean into them as much as anyone else. In recent years, it has been reported that Prince George and Princess Charlotte hilariously call Prince William 'Poachy' and Princess Kate even has a 'naughty' private pet name for her husband.
But it seems that some Palace staffers also use secret names for their royal bosses, and it was no different for Prince Harry and Meghan Markle when they were working royals. Although the couple have detached themselves from the monarchy and its protocols, while they were part of the royal family their security detail was required to use monikers for the couple. However, it had nothing to do with a desire to give affectionate nicknames to the Duke and Duchess of Sussex - these 'secret' names were created as a means to ensure their safety.
Members of the royal family are entitled to taxpayer-funded protection as public figures - something which has caused legal issues for Harry since he left the UK, as the Home Office declared he would no longer be eligible for the same security arrangements - and as part of that, security will often use secret code names to refer to members of the royal family. For example, before William and Kate were given their Wales titles, they were most commonly known as the Duke and Duchess of Cambridge, and therefore these initials (DC) were used to create new aliases for them. They would reportedly go by Daphne Clark and Danny Collins.
As per British Heritage Travel, Harry and Meghan employed a similar tactic; their security would reportedly use the code names Davina Scott and David Stevens when discussing the Duke and Duchess of Sussex. It is believed that the Prince and Princess of Wales may have adjusted their nicknames now given their newer titles, and that their code names would instead use the initials 'PW'.
So, now you know!