The Brotherhood of the Yellow Sign, also known as the Brothers of the Yellow Sign and the Cult of the Yellow Sign, is an evil cult who bore the Yellow Sign as their very own emblem and the central core of their ideology, and they are one of the many antagonistic groups featured in the Cthulhu Mythos by author H.P. Lovecraft. These people worship Hastur in his aspect as the King in Yellow.
The cult is led by a group of human immortals from the technologically and physically advanced realm of K'n-yan (the cult probably originated in this subterranean land, though others trace it to the serpent people of Valusia).
- The "Yellow Sign" which is the iconic symbol of the namesake cult, is a motif Lovecraft adopted from a story in Robert W. Chambers' The King in Yellow collection.)