EDIT The Staff of Hermes represents a staff with two wings and with two snakes twined symetrically around it. It is associated with trade and the Greek god Hermes.
A herald (caduceator) carried the caduceus (heraldstaff) as a mark of his mission. The best known carrier of the staff was Hermes who had wings on his feet, hence the wings on the staff.

The symbol evolved about 2600 B.C. and was used by the Greek priests. The alchimists of the medieval times liked to use it which makes it popular today for occult purposes.

 jsw 

EDIT Caduceus vs. Aesculapius
The Caduceus looks very similar to the Staff of Aesculapius and the two are frequently confused with each other. The Staff of Aesculapius has no wings and just one snake. In Unicode 4.1, which was published recently, the Staff of Aesculapius is encoded at U+2695.

 jsw