The sylable Om (or Aum) refers to Sanskrit. in various cultures it is holy.The sound of the OM stands ab ancient sound. It is a mantra and helps while meditating.
Om is the all-embracing and the most superior symbol of the Hindus.
Actually Om consists of 3 leters: A U M and the silence, that comes after these letters.
The parts that looks like a 3, is the A. The line that looks a bit like a snake in the right is the U. The little part on the top, that looks like a half-moon is the M. And the dot on the topis named "Bindu" and stands for endlessness, the eternal and the silence.