This symbols is well known as Pranava Mantra or OM/ AUM.It contains the numeral of 3 says that the God has in 3 forms. Therefore, He is the destroyer (Lord Shiva) He is the Sustainer (Lord Vishnu) and He is the Creator (Lord Brahman). The scientific explanation is given on my other posts says that the Universe is created by this OM sound, thus it is known as the Universal Sound and Universal Symbol. In terms of Sanskrit numerals, this 'OM'mantra is known as 786 if u see, that is the numerals used by the Muslim's previously with the symbol of Crescent, but now they refuse to use that numbers because they are afraid that Hindu's might question them. It is true that in most of the Calenders of the Muslim's there is 786 with Crescent symbolizes Islam, they cannot deny the truth.
Om is said to be the universal mantra, thus in most of Hindu's scriptures that had been written millions of years ago (Veda), each mantra or slogham's given is written with this mantra. This mantra also represents Lord Shiva.