The Heptagram (or Septegram) is a seven-pointed star, commonly associated with the occult. There are two forms: the acute heptagram and the obtuse heptagram, and both are visible in this image. The obtuse heptagram is dominant in this image, whereas the acute "elvenstar" heptagram is inscribed within.
I first came to know the obtuse heptagram by way of the band Celtic Frost, where it is featured on the Morbid Tales album cover, and also as a symbol with their Monotheist album and tour. The alt-rock band Tool also has used this symbology. The heptagram has also been used in various Christian symbology to represent the Seven Days of Creation.