The Bone King Sigil is a dark, eerie artifact with a hand-drawn aesthetic, featuring a skull motif at its center surrounded by intricate bone-like tendrils. The sigil is carved from what appears to be aged bone or ivory, with a rough, textured surface that suggests it has been weathered by time. The edges are jagged and asymmetrical, giving it a menacing, organic feel. The color palette is muted, primarily consisting of off-whites and grays, with subtle dark stains that hint at a sinister history. The sigil glows faintly with an unnatural, greenish luminescence, adding to its otherworldly and ominous presence.