'Bhasma' literally means 'disintegration'. It implies disintegration of the elements, memory, attachment and identity. It stands for the afterlife. Dattatreya & Sai Baba were often called 'Bhasmanishta' (one who loves Bhasma). This makes Bhasma all the more significant in Aghora. Bhasma is of great importance to tantriks as it serves as a reminder to them to transcend beyond mortality, to embrace death - the death of ego & to let go of all worldly desires.
Shiva is often portrayed to be covered in Bhasma as he is the embodiment of the afterlife. Bhasma is ideally cremation ash while Vibhuti is the ash from a dhuni, hawan, etc. The Bhasma aarti performed at Mahakaleshwar further validates this as Mahakal is the Lord of Death. Bathing him with Bhasma points out to the fact that the distinction between pure-impure, good-bad, light-dark, etc. does not matter. The Universe shall treat all creatures equally irrespective of anything.
The Tripundra (3 white lines) on the forehead represent the three gunas. While the red dot of kumkum stands for unleashed Shakti. The Tripundra is symbolic of the union of Shiva & Shakti (Pingala & Ida nadi at the Ajna Chakra). It is like Pralay within ourselves wherein the personal identity is lost.
Fire is the element that converts Dvaita into Advaita. Hence, it is used for cremation & sacrifices. Remains of the cremated body lay in the dual world, while the Spirit is released in the singular world. Advaita shuns Maya. Bhasma used by Tantriks & Aghoris represents the absence of Maya. Hence, Bhasma symbolizes Advaita.
In short, Bhasma stands for Death of duality and identity. When Shakti unites with Shiva (Kundalini awakening), it causes Pralay that ends the life of the Sadhak or makes the Sadhak irreversibly insane. It is the death of the feminine energy and male energy and the birth of an androgynous energy flux, the death of duality, the death of Maya!
