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.
This website is based on my research into folklore.