--similarity of a tilak symbol with lines on each side on forehead looks like a tuning fork—

--similarity of a tilak symbol with lines on each side on forehead looks like a tuning fork—

The tilak symbol you are describing is most likely the

Urdhva Pundra. Specifically, the Tenkalai denomination of the Sri Vaishnava tradition wears a Y-shaped tilak that strongly resembles the prongs and base of a tuning fork.

Wikipedia +2

Key Characteristics and Symbolism

The "Prongs": The two outer white vertical lines, often made from sacred clay called Thiruman, represent the lotus feet of Lord Vishnu.
The "Base": In the Tenkalai style, these vertical lines intersect and extend slightly down the bridge of the nose, creating the "tuning fork" or Y-shape.
The Central Line: A red or yellow vertical line in the middle, known as Sricharanam, represents Goddess Lakshmi.
Spiritual Meaning: This combination symbolizes the devotee's total surrender (Saranagati) to the Divine.
Wikipedia +3

Variations in Shape

While many Vaishnava sects use a vertical "U" shape, the specific "tuning fork" look varies by lineage:

Tenkalai (Sri Vaishnava): Distinctive Y-shape with a base extending onto the nose.
Vadakalai (Sri Vaishnava): A more rounded U-shape that sits on the forehead without the extended nose base.
Gaudiya Vaishnava: Includes two vertical lines that connect at the bottom, often with a small leaf-like shape (representing Tulsi) at the base near the nose.
Wikipedia +3

Would you like to see visual examples of the different sectarian marks to identify a specific one?



--do they mention frequency or vibrations in their worship of these deities—



While the "tuning fork" shape of the

Tenkalai tilak is primarily a symbolic representation of the lotus feet of

Lord Vishnu

, the concept of sound vibration and frequency is absolutely central to the worship of these deities.

Wisdom Library +3

In the Vaishnava tradition, the universe itself is believed to have originated from a primordial sound vibration known as Shabda Brahman. Here is how vibrations and frequencies are used in their worship:

Wikipedia +1

Mantras as Sound Frequencies: Worship involves the rhythmic chanting of Sanskrit mantras. These are not just words but "vibratory entities" intended to align the mind's internal state with sacred vibrations.
The Power of the Name: Chanting names like Krishna or
Narayana

is seen as a way to connect with the deity in "vibratory form". This practice, called Kirtan, uses music and chanting to create an immersive auditory experience designed to shift one's consciousness.

Chakra Activation: The tilak is placed exactly on the Ajna Chakra (the "third eye"). This point is considered a vital nerve center that responds to the spiritual energy generated during prayer, helping to "lock in" those sacred vibrations throughout the day.
Cymatics and Geometry: Some modern interpretations of ancient temple architecture suggest that the geometric patterns (Yantras) and temple designs were engineered to resonate with specific sonic frequencies during rituals.
Semantic Scholar +7

In essence, while the physical tilak marks your identity, the sound is the actual medium used to "tune" the devotee to the divine.

Would you like to know more about the specific mantras used to create these vibrations or the science of the Ajna chakra where the tilak is placed?