It is one of the oldest Chinese symbol, going back to the
so-called mythical epochs. According to certain
sources, it is to be merged with the Dragon-Torch,
emblem of the Yin dynasty. It is the emblem of the
lightning, it was reproduced on the royal standard
. It is the bird devoted to the blacksmith and the
solstices; in the ancient times it presided over
the days where blacksmith made the
swords and the magic mirrors.

Dictionnaire des Symboles
J. Chevalier, A. Gheerbrant, R. Laffont, 1969.