About Vibhuti 

" Holy Ash is a most sacred substance. Generally when anything is burned, the ash is dark in colour. Not so with the dung of the sacred cow when burned with milk. It burns to a clean, white ash which is regarded as holy by Hindus. Everything given by the Divine Mother in her form as Kamadenu, the milk cow, is considered as God's grace and blessing. Vibhuti has a special, godly cleansing force. When we put vibhuti on our foreheads it has the power to make the blood circulate correctly. To receive vibhuti from an enlightened soul is a rare opportunity. Such vibhuti has the power to cure diseases, solve problems, relieve physical and mental pain and nullify the effects of past deeds." 

~Swami Premananda

The ash has several symbolic meanings.

    * Placed on the forehead of devotees, it serves as a sectarian mark (tilaka). The practice of smearing holy ash on the forehead also exists in Zoroastrianism.

    * In worship connected with Lord Shiva it is a symbol of purity and is one of the main sacraments given at pūjā in all Śaivite temples and shrines.

    * The ash thus serves as a reminder to the believer to cast away selfish and worldly desires that wrap the self in maya, and calls to mind the story of how Shiva burned Kama (the god of desire) to ashes when Kama attempted to break Shiva's focus on the Divine Truth.