Ouroboros

The Ouroboros takes the form of a winged serpent bent into a ring, its tail vanishing into its own mouth so that the body closes a full circle. Set inside that loop is a hexagram, a shape long tied to alchemy and to the creation of life. The manga renders the emblem with a more stylized hexagram than the two anime series use, likely to soften any religious overtones. Most of the seven chief Homunculi wear the mark somewhere on their bodies as though tattooed there, the standout exception being Pride in the manga and 2009 anime.

As an image, the Ouroboros embodies wholeness and infinity, the perpetual turning of life into death and back again. The dragon's head reads as life's beginning while the tail caught between its jaws marks the end, and the circular motion binds the two into one unbroken cycle. Some belief systems further link the figure to a solar eclipse. Fittingly, the emblem can be viewed as a kind of template for the transmutation circles that run through the series, and Edward once labeled the mysterious figures behind Amestris's troubles the Members of the Ouroboros before their true nature came to light.

Each Homunculus bears the mark in a place of its own. Across every version of the story, Lust carries it on her sternum, Gluttony on his tongue, Envy on the left thigh, and Greed on the back of his left hand. The manga and 2009 anime set Wrath's on his left eye and Sloth's on his right shoulder, while Pride alone lacks the emblem, showing instead a circular sign on his true form's forehead. The 2003 anime rearranges several of these, placing Wrath's on the sole of his foot, Sloth's near her heart, and Pride's on the left eye.

The symbol carries extra weight in the first anime, where stripping a Homunculus of its tattoo can reduce the creature to a mindless slave of its own sin, as befalls Gluttony once his mark is removed. A bitter irony threads through it all: the Ouroboros evokes magic and regeneration, yet the Homunculi themselves cannot perform alchemy, and the endlessly self-renewing imagery cuts sharpest against Wrath, who cannot regenerate at all.