It may be thought of as a symbol of rebirth. This snake features strongly in Aztec religion
"Hydra"
双頭の蛇 /sou tou no he bi/ means 'two-headed serpent' in Japanese.
Hercules the demigod and warrior
The double-headed arrows on polarizers and analyzers represent the direction of polarization that they allow to pass through their material. It indicates that light with polarization parallel to the arrow direction can pass through, while light with perpendicular polarization is blocked.
Hydra was a many headed serpent in Greek mythology
A serpent represents temptation. This is a representation that comes from the biblical story of the Garden of Eden, with the serpent tempting Eve.
Some Toltec symbols include the feathered serpent Quetzalcoatl, the jaguar as a symbol of power and strength, and the double-headed serpent as a representation of duality. Other symbols in Toltec art and culture include the sun, the moon, and various geometric designs.
The Yellow-headed Amazon (or Double Yellow-headed Parrot) comes from Mexico and Northern Central America.
See related links for a picture of a cursor double-headed arrow.
On the drawing toolbar, go to autoshape->connectors, and the double arrow is in there.
1} Double headed eagle is of the Prussian orthodox christian church , representing a time where once Christendom was divided in West & East , after much persecution , this emblem found itself in Russia. 2}The fish , is the secret sign of Christians 3}And the serpent is the EVIL it battles & conquers !