A request by Sri Swami Vishwananda:
Anyone who regards himself as His devotee should now wear a Tilak during Darshan and other main events.
Here's the general meaning:
The Tilak is a sign of good luck. It is worn on the forehead and is composed of sandalwood paste, sacred ashes and/or kumkum.
In the Bhagavad Gita it says: "A forehead without a Tilak, is like a heart without mercy, or a fountain without water, or a village without a temple, a flower without fragrance, or a field without rain...(there are still many more examples.) It can be seen that this ancient tradition of the tilak clearly has a deep spiritual meaning.
Today one wears a tilak in the temple or during special occasions such as religious ceremonies.
The Tilak is applied on the Ajna Chakra, the space between the two eyebrows more commonly known as the third-eye. It is said to have a cooling effect during meditation and it helps one to open his/her third eye immensely. All intellectual influences and spiritual effects aside, sandalwood also possesses great medical value.
There are two main types:
Shaivite Tilak is worn by the followers of Lord Shiva. It consists of three horizontal lines on the forehead with a vertical band connecting them. This particular Tilak consists of holy/sacred ash. (Vibhuti)
Vaishnava Tilak is worn by the followers of Lord Vishnu. It consists of a long vertical red line from the third-eye to the hairline and is bordered by two additional vertical lines. The two outer lines (from sandalwood/chandan) represent the Lotus feet of Lord Narayan. The red line (from kumkum) represents Lakshmidevi. In addition to this another spot of sandalwood in the shape of a Tulsi leaf is to be applied underneath the U-shaped Tilak as a sing of worship to Goddess Tulsi. Swamiji has also asked that we place a small red dot of kumkum inside the Tulsi leaf to simbolise the presence of the Guru in one's life and spiritual path.
When applying the Tilak a Mantra is traditionally spoken, which says "Oh Lord, protect me from the evil consequences of the Maya, and save me from all worldy ties" - or simply:
"Om Namo Narayanaya"
The Pope also received a Tilak during a ceremony when he visited India.
Here is a short video of the HareKrishnas as a guide on how to apply the Tilak in an easy and simplistic way:
(The central red line is simply the end of an incense stick and damp kumkum drawn along from bottom to top.)