Hindus apply Tilak on the forehead between the two eyebrows. It is a straight line of Kumkum applied with the thumb from down to up. So, it is broadened at the bottom and pointed on the top. Tilaks come in different shapes. Some people use a U-shaped white Tilak. Generally ISKCON members apply this type of Tilak. A round-shaped Tilak which looks like a bindi is also very popular. Women also apply this type of Tilak. Generally, those who worship Lord Shiva apply three horizontal lines of holy ash across the forehead with a round spot of sandal or kumkum in the middle.
In the world, only Hindus apply Tilak. Hence, it is an identity for Hindu males and is a symbol of Hinduism. You would see some Hindu deities with Tilak marked on the forehead. Tilak symbolizes third eye, which is associated with spirituality.
The colors of Tilak vary from region to region and castes to castes. The common colors of Tilaka are red, orange, combination of red and white, and yellow. Sandal paste is also used for Tilak.