Everything in the world of Evorstrom is classified by Sign; society, culture, food, religion, government and even art.
The relationship between Signs dictates not only what people can eat but how their culture treats people of differing Signs. There is actual, measurable antipathy between opposing Signs and a near mindless sense of devotion to the people and places of a persons' own Sign.
Long ago a system of governance was enacted by a particularly benevolent Scion that aligned all eight Sign governments and religions under a single pact that helped curtail violent conflict between opposing Sign civilizations.
Every five years one Sign is declared "ascendant" and is granted tie-breaking voting power on the Council of Lords. When their term ends the next Sign (moving clockwise) on the Circle is granted ascendancy.