Flamel

The Flamel refers to the mystical and alchemical symbol depicted as a cross with a snake or serpent draped about it, as well as detached wings and a crown above it.

It resembles and shares common origins with many ancient symbols (which it is often mistaken for), such as the Rod of Asclepius (the ancient Greek sign of medicine), the Caduceus (the ancient Greek symbol related to the god of Alchemy, Hermes ) and the Nehushtan (a Hebrew sign signifying victory over the devil). It is also one of the symbols attributed to the medieval professed French alchemist, Nicolas Flamel. The cross appears in Flamel's grave illustrations and many say to symbolize Flamel's relation to the Philosopher's Stone.

In Alchemy, the Flamel represents the "fixing of the volatile", a vital step in the alchemical opus' process, related to the making of the mercury's elixir and of curative processes.

In the Fullmetal Alchemist series, the Flamel symbol is the mark depicted (along with wings and a crown above it) on the back of Edward Elric's trademark red coat and on the left shoulder of Alphonse Elric's armor body. Though the manga does not explicitly state how the mark is significant to the Elric brothers, their alchemy teacher, Izumi Curtis also bears the mark, tattooed on her left breast, suggesting that the brothers share their master's alchemic symbol to show their tutelage under her.

In the 2003 anime series, Izumi states that the mark is that of her alchemy teacher, Dante. Above Dante's wooden chair in the library in her house, there is a golden statue of this symbol. Also, the Transmutation Circle used to weaken Homunculi is centered around this design.

Another theory of what it could mean is that the symbol refers to alchemists who have attempted human transmutation, since all of the above characters  who have this symbol have attempted human transmutation previously. This however can be discredited in episode 12 of Fullmetal Alchemist Brotherhood, when the Elric brothers visit Izumi. Izumi transmutes a spear to surprise attack Edward, forcing him to transmute his automail that he is keeping hidden with his glove. The Elric brothers sound surprised when Izumi states she could tell they had committed human transmutation by sparring with them, knowing all along Alphonse was an affixed soul and Edward was missing limbs as a result of attempting human transmutation. Throughout this time Alphonse has the Flamel on the shoulder of his armour, which Izumi would have noticed immediately, resulting in this scene being pointless if the mark was an indication of committing taboo.

Trivia

 * This symbol can also be seen in the movie Paranormal Activity 6: The Ghost Dimension on one of the computer screens, although it is not known if the symbol alludes to the one used in the Fullmetal Alchemist series.
 * The symbol can be seen on the wall in the movie The Veil. This one has the same crown and wings as seen in the FMA series.The-veil-flamel.png