have traditionally used this
symbol for the planet Mercury, and it is the medieval alchemical
sign for the element mercury (Hg) as well. It consists of the biological
sign for female (the sign used for the planet Venus), but topped
with “horns” or a crescent. Mercury was the swift messenger
god of classical Roman civilization, and the horns represent the
winged hat he is usually shown wearing. In ancient Greece, he was called Hermes.
The god Mercury was also symbolized by a caduceus - a staff
with two snakes wound about it. The caduceus is today occasionally
used to represent medicine, but the true symbol for medicine is
the staff of Aesculapius (the Greek god of medicine and healing)
which has only one snake.