“Unlike other celebrities, however, the Queen has never been allowed to sign her autograph.
“In fact, the entire Royal Family is banned from signing their names for fans.
“This is in case their signature is forged later on.”
Ms Liwag Dixon added: “Now there have been a few rare instances, in which other royals have broken this rule.”
The List video showed a picture of the Duchess of Sussex signing a flag for a fan during walkabout outside Cardiff Castle.
This had happened in 2018 when she was still only Prince Harry’s fiancée.
The pair had made the trip to Wales as their third royal visit as a couple.
The narrator told viewers this was “simply because Queen Elizabeth’s signature is so rarely seen”.
Taking selfies is another rule that the Queen has banned.
Although royals have been known to sometimes snap pictures with those who have come out to see them.
This is, again, based on fears about fraud.
It is possible that some posing could be used to commit identity theft.