Prince Andrew was targeted by a bus stunt urging him to "call the FBI" to discuss the investigation into Jeffrey Epstein.
A yellow American school bus bearing a picture of the Duke was driven past Buckingham Palace on Friday.
On its side, a message read: "If you see this man please ask him to call the FBI to answer their questions.”
The Standard has contacted Buckingham Palace for comment.
The action was coordinated by Gloria Allred who represents some of the victims of sex offender Epstein, who died in a prison cell last year as he awaited trial over trafficking charges.
She said Andrew had a duty to speak to the bureau, while some of Epstein's accusers have also pushed for him to assist in the posthumous investigation into further allegations that were levelled against the sex offender.
His death was ruled a suicide.
Andrew has been questioned over his links to Epstein, having been friends with the disgraced financier.
He stepped down from public duties last year over following a disastrous Newsnight interview where he was probed on their relationship.
Some accusers have also made allegations towards Andrew - all of which he has vehemently denied.
