Daejonggyo (대종교 / 大倧敎), usually anglicized as Daejongism, is a religion in South Korea, founded in 1909 as a revival of Korean Shamanism.
According to the official Deajonggyo website (http://www.daejonggyo.or.kr/main/?skin=comp_flag.htm, in Korean), Daejongism originally used a flag [presumably white] with a blue disc bearing the hanja (Chinese character) "神" (God) in white.
The current Daejongist flag, known as the Cheonsingyogi (천신교기 / 天神敎旗 "Heavenly God Religion Flag"), is white with a blue disc bearing a yellow square, in turn bearing a red equilateral triangle. The symbol represents philosophically Heaven-Earth-Humans, and theologically God-Humans-Materials.

This flag was adopted on January 16 1926, but due to Japanese persecutions against the Korean independence movement (to which Daejongism belonged) it was not actually used until December 26 1935.
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Takuyakoz