Chinese mythology
The Chinese dragon is one of the most important mythical creatures in Chinese mythology, considered to be the most powerful and divine creature and the controller of all waters who could create clouds with their breath. The dragon symbolized great power and was very supportive of heroes and gods. The conventional dragon has a certain description, however there are other dragons or dragon-like beings that vary from this description. For example, the Chi of mythology lacks horns. Dragons often chase or play with a mystical or flaming pearl. A dragon-fenghuang pairing is a common motif in art, the fenghuang often being called a "phoenix".
Chinese numismatic charm
Another hypothesis on why star, moon, cloud and dragon symbols started appearing on Chinese cash coins is that they represent Yin and Yang and the Wu Xing, or more specifically the element of water (水), this hypothesis claims that the appearance of these symbols wasn't accidental but a manifestation of the fundamental belief of the ancient Chinese people of the time in Yin Yang energy and the elements of the Wu Xing. The Hanzi character for a "spring" (泉), which in this context refers to the underground source of water also meant "coin" in ancient China. In Chinese mythology the moon was an envoy or messenger from the heavens and water was cold air of Yin energy that was being accumulated and had their origins on the moon. As the moon was the spirit in charge of water in Chinese mythology and was in fact its essence the alleged meaning of crescent symbols representing "the moon" on cash coins could indicate that cash coins have to circulate just like water which flows, gushes, and rises. The symbolism of "clouds" or "auspicious clouds" in this context may then refer to the fact that clouds cause rain, in the Book of Changes the second trigram is mentioned to be representative of the element water which appear in the heavens as clouds, this would also imply that like flowing water cash coins should circulate freely. The appearance of wiggly-lines that represent Chinese dragons happened around this time as well and may have also been based on the Wu Xing element of water as dragons were thought to be water animals that were the bringers of both the winds and the rain, this would also confirm that dragons represented the nation that the circulation of cash coins should be free akin to how water flows. In later Chinese charms, amulets, and talismans the dragon became a symbol of the Chinese emperor as well as the central government of China and its power.