The most important Hindu symbol is called Aum, or Om. It has three syllables, which are central to its meaning, and whose sound is considered to be the greatest of all mantras.
The three vowels in the Hindu symbol Aum represent many things; however, they most notably represent the three states of consciousness: waking, dreaming and deep sleep. The whole symbol, on the other hand, represents the fourth state, which is awareness of one's spiritual identity.
It is also supposed that the trisyllabic word symbolizes earth, atmosphere and heaven. It could also symbolize the three major Hindu gods, or the three sacred Vedic scriptures.