This is a roughly inked version of the Yellow Sign, based on the design from the early printings of "The King in Yellow" by Robert W. Chambers. The depiction of the King on the cover of those editions has been copied by hundreds of artists, but only a handful have used the inverted torch featured on both the front cover and the spine. Based on it's historical usage I think there's a strong case to be made that it's not just a random decorative element, but a depiction of the Yellow Sign. You can find more information on the subject, including the Sign's uncanny resemblance to an inverted Rod of Asclepius, in the Arkham Sanitarium post from earlier this week.
Before anybody asks, yes, I'm familiar with the three armed design created by the very talented Kevin Ross. He's a wonderful artist and I greatly admire his work, but he's open about the fact that his depiction is solely the product of his imagination. I prefer this alternate interpretation solely because of it's historical ties to Chambers' work.