The person with a star, sun or moon on their face appears in several different tale types. However, depending on the tale, the details are a little baffling. What does having a star on your forehead even look like? Is it a literal star? Is it some kind of crown? Is it a birthmark shaped like a star?
The unusually-decorated girl appears in The Twelve Brothers (Germany), "The unnatural mother and the girl with a star on her forehead" (Mozambique), and The Maiden with the Rose on her Forehead (Portugual).
In some versions of Aarne-Thompson-Uther type 850, "The Birthmarks of the Princess," she has birthmarks shaped like stars, suns, or moons.
Sometimes, in the tale of "The Kind and Unkind Girls," the star is a reward given to a generous young woman. Her selfish and greedy sister receives horns, a donkey's tail, or some other ugly object on her forehead. I read one where it was a sausage.
Examples of this variation include:
The last tale type that is well-known for the forehead-star is ATU type 707: The Three Golden Children. A woman gives birth to marvelous children, who have unusually shiny characteristics.
The star functions as a tangible sign of royalty and/or virtue. If a color is given, it is usually gold. Golden hair or skin can appear in similar roles, instantly marking someone as beautiful and extraordinary.
Researching folktales and fairies, with a focus on common tale types.