This is another of
the earliest ideograms used by humans in this cycle of civilization.
It was associated with the idea of divinity and power. Later, has been used in
Buddhist art to indicate charisma, the emanation of spiritual
power from a person, the halo. As a halo it has also been used in Christian
symbolism, although the ancient sun symbol is more
common for that purpose in Christian art.
This sign has also been used as an anti-Semitic symbol (compare with ). At the Fourth Lateran Council in 1215 it was decided that Jews should wear high pointed hats to distinguish them from others. Some years later the yellow ring was invented for the same purpose. (Note that when is used as a halo in Buddhism it is usually yellow or orange.) There was instructions as to how the yellow ring was to be worn worked out, for example, in Reichstadt Frankfurt in 1452.
A few modern uses of this sign: calm in meteorology, temporary runway in aviation, and here they give you food and money in the British and Swedish systems of hobo signs.