The Necronomicon --fictional Grimoire, folk myth, or suppressed text-- has inspired countless tales within the Cthulhu Mythos Cycle, and was first mentioned by H.P. Lovecraft in his short story, 'The Hound'.
Here we have my own take on the Sigil of the Gates, a symbol drawn from this unspeakable tome, and a sure means of inviting the power of the outer universe into your own domain.
"Nor is it to be thought...that man is either the oldest or the last of earth's masters, or that the common bulk of life and substance walks alone. The Old Ones were, the Old Ones are, and the Old Ones shall be. Not in the spaces we know, but between them, they walk serene and primal, undimensioned and to us unseen. Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth. He knows where the Old Ones broke through of old, and where They shall break through again..."