To a yogi, no symbol is more powerful than the syllable OM, as witnessed by these words from the Mandukya Upanishad:
OM: this eternal word is all what was, what is and what shall be.
In the Sanskrit letter the long lower curve represents the dream state, the upper curve stands for the waking state and the curve issuing from the center symbolizes deep, dreamless sleep.
The crescent shape stands for Maya, the veil of illusion, and the dot for the transcendental state.
When our individual spirit passes through the veil and rests in the transcendental, we are liberated from the three states and their qualities.