Its the sign of Asclepius, the Greek god of healing, and a serpent-wrestling hero, Heracles, Phorbas of Rhodes or some other.
The snake is a symbol of earth in ancient Greek tradition. So it should be an earth sign.
Although I don't know how you could genuinely add it to the zodiac. What do you base the readings on? The basics of astrology, at least, are described in the 2000 year old book by the Greek Dorotheus and the Roman Julius Firmicus Maternus. But there are naturally no ancient readings connected with Ophiochus.