Don't Tread on Me Flag (Gadsden Flag)
First flown aboard a Colonial Troop ship on January 4th, 1776
This was the flag of the American Colonies at the time of the American Revolution against England.
It features a rattlesnake above the warning, "DON'T TREAD ON ME". The rattlesnake had become a traditional symbol of the American Colonies. The most obvious reason for this is that the rattlesnake was only found in the American Colonies (and in abundance, to the dismay of settlers) and nowhere else in the world. The origin of the slogan (Don't Tread On Me) pertains to the snake's deadly strike and the idea that it is best to leave them alone.
The snake on the flag is also roughly arranged in the shape of the American Colonies with the tip of the tail being the Florida peninsula and the head being New England.