According to Osho, Om was chosen because a sign was needed that carries no fixed meaning—pointing beyond mind and language to the seventh plane. Formed from the root sounds A‑U‑M, it’s rendered as a pictorial glyph (not letters) whose three parts mirror those phonemes. In thought‑free awareness (the fourth body), their natural confluence is heard as Om, an inner primordial resonance.
Om is a sound made of A, U, and M, shown as a picture so no one fixes a meaning to it, and when your thoughts fall silent you can sense it inside.