A constant intriguing factor in the imagery of the Great Buddha is the group of three curving conch-like lines on his neck. In the varied world of Buddhist art this is one common characteristic that shines across all aesthetic traditions. Like other Buddhist motifs, it too is soaked in rich spiritual symbolism. It is said to represent Buddha’s deep and resonant voice, through which he introduced his followers to the path of dharma.

The association of the conch shell with Buddha’s melodious voice, sweet with the tenor of his uplifting message, has both an archetypal simplicity and universal appeal. It is a hard-hitting symbol which associates a primordial object (deemed sacred in all ancient traditions) with the actual physical body of the Buddha. Indeed, though much of Buddhist philosophy is esoteric, when it comes to aesthetics, Buddhist art is justly famous for giving a physical, easily recognizable representation to abstract philosophical truths.

via The Eight Auspicious Symbols of Buddhism – A Study in Spiritual Evolution.