In the earlier days, different colour tilaks were worn by different people belonging to different castes. The Brahmins wore 'White Chandan or sandalwood' signifying purity for their engagement in priestly or academic vocations. The
Kshatriyas wore a red tilak signifying valour of the warrior class. The Vaishya's adopted a yellow kesar or turmeric mark signifying their involvement in trade in the creation of wealth. The Sudras wore a black tilak to represent their unmatched service in supporting the work of all the other sections.
The Vaishnavas or the devotees of Lord Vishnu wore a sandalwood paste in the shape of a 'U', while the devotees of Lord Shiva smeared their forehead with the holy ash or 'Bhasma'. The devotees of Devi or the divine mother wore a red mark, Kumkum.
The striking mark on the forehead not only calls for beauty but also goes in for a wider connotation. The tilak serves as a covering for the spot between the eyebrows which is supposed to be the seat of memory and thinking. The spot is called the Ajna chakra according to the language of Yoga. The application of the tilak is done with the prayer "may I remember the Lord. May this pious feeling pervade all the activities I am involved. May I be righteous in my actions" . The mark brings us back the prayerful attitude even if one forgets the Lord on and off in the daily chores.
There is another important significance of wearing of the tilak by Hindus. The whole body is supposed to send forth energy in the form of electro magnet waves especially the spot in between the eyebrows. This forms the reason for worry to generate heat causing headache. The tilak thus cools the forehead and protects from the seepage of energy which the fashion sticker bindis normally do not support.
Hence tilak is considered as not only a religious mark but also to safeguard one against negative tendencies and forces.