Circle with a Dot or Circumpunct
The circle with a dot in the center is perhaps one of the simplest and most incredible of symbols. The circumpunct has been used for an incredibly long time. The symbol once was a representation of the sun, and as such as been the symbol to represent the Archangel Michael. The circumpunct is also the alchemical symbol for gold.
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Perhaps the most profound meaning for the circle with a dot in it is that of God. I had a professor once who had asked the class to draw the best representation of God. There were some students who drew Christ, others an old man in a chair, and then there were some that drew the Hindu gods. In the end all he did was draw a circle on the board with a dot in the center.