The first known use of the pattern dates back to 430 A.D. in the shield patterns of the Roman army. The Roman pattern matches the S-shaped pattern of the classic yin-yang, which is the Chinese symbol called taijitu. The symbol itself is formed by drawing two circles along the diameter of a third larger circle, and erasing parts of the circles so that only the S-shape remains.
The only difference in the Roman version of the yin-yang pattern is in color. The shields dating furthest back in Rome come from an infantry unit called the shield bearers or armigeri defensores seniores. The symbol is also represented in later Roman military units such as the pseudocomitatenses, another Roman military unit, as well as other infantries.
In fact, Chinese use of the yin-yang pattern occurred several hundred years later and date back to about 11th century A.D. The pattern is also seen in Celtic and Etruscan history.