Chances are you’ve come across a mon (or kamon) during your time in Japan, even if you weren’t aware of it at the time. Mon are symbols used to identify different families of clans in Japan, similar to the coat of arms of European aristocracy. From the chrysanthemum crest of the royal family to the Tokugawa’s hollyhock, mon are an artistic and integral piece of Japanese history and culture.
Mon have been around since at least the 9th or 10th century and were originally only used by upper class families. Mon were emblazoned on battle standards and used at temples affiliated with certain clans. The crest of the Taira clan (also known as the Heike) is one of the more well-known designs, and their stylized butterfly symbol can be found on many things in villages that claim to descend from this upperclass family that lost the Battle of Dan-no-ura in 1185 and fled for their lives.
There were a few rules regarding mon that most Japanese adhered to in previous centuries. You never “stole” or borrowed the design of another family (not without knowing, at least) and if you came into contact with a clan who had the same or a similar design, the lower-ranking person would often change their crest. In my home prefecture of Kumamoto, when the Hosokawa clan took over control of the Higo domain (which is mostly present-day Kumamoto Prefecture), they actually merged their crest with the previous rulers (the family of notable samurai Kato Kiyomasa), allegedly as a means of honoring Kato’s vision for the land he governed.
Today, you’ll find mon on buildings owned by the Imperial Family (the many-petaled chrysanthemum), on the packaging of certain traditional products (rice crackers, tofu, sake) and on the roof tiles of old samurai villas or shop buildings. Mon have also been used on kimono for many centuries, and the tradition continues today.
You can get a good look at a number of mon at this link and use it as a guide when you’re scouring Japan for clan symbols.