The rules are strict: the British royal family is prohibited from signing autographs.
The code of good conduct of the British monarchy states that no member of the reigning family should sign autographs.
According to The Express, no one is authorized to sign a document without first obtaining the Queen’s consent.
This rule applies of course to the most famous figures in the family: the Duchess of Cambridge, née Kate Middleton, Prince William and Prince Harry.
The reason is simple and logical: in order to avoid any risk of falsification of their signature and therefore any usurpation of identity.
So put aside any hope of ever seeing Duchess Kate scribbling her signature on a picture. Fortunately, we still have the selfies.