Jai Jai ShriGokulesh,
Firm faith in Shri Krishna, devotional sentiment, the renouncement of refuge in other gods and the initiation of the surrender can be said as the internal characteristics of being a Vaishnava. Whereas, Tilaka, Mudra, Cakra-Gada-Sankha-Padma and the Tulasi-Mala could be considered as the external marks of the Vaishnava.There are numerous religious sects in Bharata. The believers in Shiva draw Tripundra on their foreheads. The believers of Goddesses draw Tika on their foreheads, while the devotees of Hanuman apply Sindura. Likewise, Shri Vallabhacharya has stated in his work “Sarvanirnaya-Nibandha”:
Sankhacakradikam dharyam, mrda pujangameva tat;
tulasikasthaja mala, tilakam lingameva tat.
Conch disc et cetera be held, With clay on the upper arm;
The garland of tulsi in the neck, And Tilak-Mudra on the forehead.
Meaning: The male Vaishnavas should apply the marks of Tilaka, Mudra, Sankha etc. on the forehead, on the upper arm and on the different parts of the body with Gopichandana and Kumkum, and should wear garland-wreath, made of Tulasi-wood, in the neck.
Thus, it can be seen that the external marks are different in all sects. As a uniform is an identification of a school, the external marks serve the purpose of identification of the followers of different sects. At the same time these marks contain certain devotional and divine sentiment. For example, Tilaka is a symbol of the feet of Shri Krishna. It reminds of one's Dharma and self-surrender to Bhagavan.
Tilaka: The Vermilion vertical mark of ‘U’ & '||'shape on the forehead.
Mudra: Mark of Mantra.
Cakra-Gada-Sankha-Padma : Weapons & other holdings of Vishnu: wheel with sharp edge, mace, conch and lotus respectively.
Tulasi-Mala: The Tulasi-Garland.
Tripundra: The ash-mark on the forehead with three horizontal lines.
Gopichandana: Clay of the Gomati river.
Kumkum: Red turmeric powder / saffron.
