OUROBOROS

From WICKED: The Grimmerie, a Behind-the-Scenes look at the Hit Broadway Musical.

When I first saw this symbol I immediately recognized the snake from an X-Files episode. In the 13th episode of the fourth season ("Never Again") Scully has an ouroboros tattooed on her back to symbolize a new beginning in her life. 
I didn't particularly like this episode -- it was one of those all-about-Scully episodes, aka no Mulder -- but I welcome any reference to one of my favorite television series! And it sparked curiosity for me and led to some interesting investigation!

In Egypt, the first known appearance of the ouroboros motif is in the Enigmatic Book of the Netherworld, an ancient Egyptian funerary text in KV62, the tomb of Tutankhamun, in the 14th century BC. The text concerns the actions of the god Ra and his union with Osiris in the underworld. 

Gnostic gem from Roman-era Egypt (1st century AD), with an ouroboros surrounding a scarab and voces magicae, characters representing magic words.

In alchemy, the Ouroboros is a sigil -- a symbol used in magic. The term has usually referred to a type of pictorial signature of a demon or other entity; in modern usage, especially in the context of chaos magic, it refers to a symbolic representation of the magician's desired outcome.

Early alchemical ouroboros illustration. From the work of Cleopatra the Alchemist (Greco-Roman Egypt).

Within Kundalini Yoga, ouroboros symbolism has been used to describe Kundalini energy. According to the second century Yoga Kundalini Upanishad, "The divine power, Kundalini, shines like the stem of a young lotus; like a snake, coiled round upon herself she holds her tail in her mouth and lies resting half asleep as the base of the body" (1.82). Another interpretation is that Kundalini equates to the entwined serpents of the caduceus of the Greek god Hermes, the entwined serpents representing divine balance in the west or, esoterically, human DNA.

Kundalini chakra diagram