The Elven Star or the 7 pointed star has many different uses. One is to keep secrets safe from prying eyes of other magicians.
People sometimes wear it as an amulet to keep people from reading their mind. You could also use it on a book of spells to keep people from understanding, or knowing the true nature of the contents.
It is also used to symbolize communities that identify as spiritually nonhuman (Otherkin or Otherkind), beginning with the Silver Elves and Elf Queen's Daughters in the early 1970s.