The Unkillable Sigil is a dark, intricately designed emblem with a hand-drawn aesthetic, featuring a central skull motif surrounded by swirling, arcane patterns. The sigil is etched into a weathered, aged metal plate, with a slightly raised surface that gives it a tactile, engraved feel. The colors are muted, primarily blacks and deep reds, with faint glowing accents that suggest a sinister, magical energy. The overall design is symmetrical but with intentional imperfections to enhance its eerie, otherworldly appearance.