The Mark of Destiny is a magical symbol by which the Chosen One spoken of in the prophecy of the Ancient Scroll would be known.
In truth, three people are known to bear the Mark; Rohan, who is the Chosen One, as well as his half-brother, Lugad, and their mother, Queen Maeve of Temra. It is not known if there is any special significance to Lugad or Maeve bearing the Mark, other than it signifying their kinship to Rohan.