If the player travels to one of the corners of map, far out to sea, a large brown sign will appear underwater, inscribed with the phrase Here Be Dragons! in the classic medieval style font.
The sign is a clear reference to old European folklore, which theorized that unexplored areas of the earth, such as those along the coast of the Americas and much of the Atlantic Ocean, were home to great mythological beasts. This is illustrated by the frightening imagery seen on maps and globes of that time.
However, the game doesn't feature an illustration of a dragon, nor is it likely that an actual dragon appears within the game. It is possible that those "Dragons" are in fact some chinese street gangs.