The snapper was waiting to take pictures of Styles outside his home in London and asked him to sign something for his Daughter Ella.
The singer then proceeded to scrawl the joke text onto a piece of cardboard from his car before handing it over, reported Sun Online.
The autograph read: "To Ella, please tell your daddy to go away. Love from Harry x."
Styles, 18, has just returned from a promotional trip to France with the rest of his 1D band mates.