In Vaishnava temples, Theertham, Satari and Thulasi are the three common things that a devotee is offered. After the Theertham is given, the devotees bow down their head to get the Satari. Satari is said to be the form of Sri Nammalwar, who is also named as "Sadagopan". As Sri Nammalwar says in his Thiruvaaimozhi, that all our sins will vanish if we strongly attach ourselves to the divine feet, the thiruvadi of Sriman Narayanan. He also explains that this is the universal way of attaining Mukthi (Moksham). Since, his teachings can't reach all the people in this world but at the same time, they too also has to be shown the way to attain Mukthi, Sri Nammalwar himself is found as "Sri Satari" in all Sri Vaishnavite temple. In the Sri Satari, we can find the thiruvadis (two feet at the top of the Satari), which are said to be the feet of Sriman Narayanan and this says that Sri Nammalwar is holding the Thiruvadi of Sriman Narayanan on his head. Because of this only, we should bow down our head to get the Satari on our head. And this is the regular custom that is followed in every Vaishnavite Temples