Why do we wear marks (tilak, pottu and the like) on the forehead?

The tilak or pottu invokes a feeling of sanctity in the wearer andothers. It is recognized as a religious mark. Its form and colour varyaccording to one's caste, religious sect or the form of the Lordworshipped.In earlier times, the four castes (based on varna or colour) - Brahmana,Kshatriya, Vaishya and Sudra - applied marks differently. The brahminapplied a white chandan mark signifying purity, as his profession was ofa priestly or academic nature. The kshatriya applied a red kumkum marksignifying valour as he belonged to warrior races. The vaishya wore ayellow kesar or turmeric mark signifying prosperity as he was abusinessman or trader devoted to creation of wealth. The sudra applied ablack bhasma, kasturi or charcoal mark signifying service as hesupported the work of the other three divisions.Also Vishnu worshippers apply a chandan tilak of the shape of "U,"Shiva worshippers a tripundra of bhasma, Devi worshippers a red dot ofkumkum and so on).The tilak cover the spot between the eyebrows, which is the seat ofmemory and thinking. It is known as the Aajna Chakra in the language ofYoga. The tilak is applied with the prayer - "May I remember the Lord.May this pious feeling pervade all my activities. May I be righteous inmy deeds." Even when we temporarily forget this prayerful attitudethe mark on another reminds us of our resolve. The tilak is thus ablessing of the Lord and a protection against wrong tendencies andforces.The entire body emanates energy in the form of electromagnetic waves -the forehead and the subtle spot between the eyebrows especially so.That is why worry generates heat andcauses a headache. The tilak and pottu cools the forehead, protects usand prevents energy loss. Sometimes the entire forehead is covered withchandan or bhasma. Using plastic reusable "stick bindis" is not verybeneficial, even though it serves the purpose of decoration.