Identical to the Western symbol for the Sun Cross, the Kamon is a medieval family crest from Japan
In Japan ka means 'family', mon means 'crest' and this symbol is one such family crest. Like European heraldry, kamon were used especially in battle to identify individuals or members of a clan. They were first owned by the aristocracy and later rolled out to anyone associated with that community.
Kamon are still used by Japanese, especially as decorations on formal kimono. As with Western heraldic arms, there are hundreds of different designs and the name of this particular kamon is kutsuwa.
The symbol was originally meant to represent the mouthpiece of a horse's bridle (bit) – although how became remains a bit of a mystery. More convincingly are the records of the Shimazu samurai of Kagoshima who also used this symbol. They simply encircled the Japanese kanji character ju (ten).
The last samurai of Kagoshima was Saigo Takamori (1828-77). He is considered the very last warrior samurai of Japan and was the basis of the 2003 movie The Last Samurai. Saigo is seated in the print (above) and the kutsuwa-mon is clearly seen in his banners.
Interestingly, Kagoshima was an early and significant centre for Christian activity. When Christianity was forced underground in Japan (see the incredibly brief potted history of Christianity in Japan), Christians developed a secret method to identify themselves to each other.
In the West, Christians forced into hiding used the Anchor Symbol as their secret identifying symbol. In Japan, they used the Kutsuwa symbol, since this so closely resembles a Christian cross.
See also Sun Cross.