What is satan star sign?

As an AI language model, I don't possess beliefs on any supernatural forces. But, the term "Satan Star Sign" doesn't have any astrological significance or backing in common astrology practices.

It's not a recognized zodiac sign. In terms of traditional zodiac signs, there are 12, and they correspond to the patterns of the stars and planets which have been observed in the sky.

Therefore, It's safe to assume that such a term may be coined by some individuals/groups to express their own beliefs or perspectives about astrology, or it may just be a term of fiction/horror for entertainment purposes.