I opened the box. On the pink cotton inside lay a clasp of black onyx, on which was inlaid a curious symbol or letter in gold. It was neither Arabic nor Chinese, nor as I found afterwards did it belong to any human script.
- "The Yellow Sign" by Robert W. Chambers

First published In 1895, The King in Yellow by Robert W. Chambers is a collection of short stories loosely connected by the presence of a banned book, an infamous stage play entitled "The King in Yellow." These stories describe the plights of certain sensitive and creative people who have fallen under the spell of this mysterious tome or the alternate, somewhat psychedelic, world that it describes. The stage play is comprised of two acts: the first of banal innocence, and the second of unutterable madness that can drive the reader to insanity or hopeless despair. It tells the tale of the mystical King in Yellow, who wears tattered yellow robes, the fabled city of Carcosa, the lake of Hali, and of the mystery of the Hyades. Some believe that this abominable book was the inspiration for H.P. Lovecraft's own Necronomicon, another book of sanity-shattering truths, though there is some controversy about whether Lovecraft had read Chambers before inventing the famous Necronomicon of the Mad Arab.

The Yellow Sign is the symbol of the King, and when shown to the right kind of person - someone sensitive to it, either through madness or art - it reveals irresistable truths and ensures allegiance to the mysterious King of this otherworld.

I showed him a list of thousands of names which Mr. Wilde had drawn up; every man whose name was there had received the Yellow Sign which no living human being dared disregard. The city, the state, the whole land, were ready to rise and tremble before the Pallid Mask. The time had come, the people should know the son of Hastur, and the whole world bow to the black stars which hang in the sky over Carcosa... I had a blank bit of paper in my pocket, on which was traced the Yellow Sign, and I handed it to him. He looked at it stupidly for a moment, and then with an uncertain glance at me, folded it with what seemed to me exaggerated care and placed it in his bosom.
- "The Repairer of Reputations" by Robert W. Chambers

The Yellow Sign itself is never described in more detail, so its exact appearance remains unknown (except to those who are under its spell). However, the most popular and recognizable version of this tainted symbol was designed in 1989 by artist Kevin Ross for Chaosium's Call of Cthulhu roleplaying game. [view original article here] http://www.barnesandnoble.com/w/the-king-in-yellow-and-other-horror-stories-e-f-bleiler/1005230973?ean=9780486437507