All Hindu temples have a flag and are hoisted mainly during festivals and auspicious days on a Dwaja Stambha. But in North India , flags are a constant feature of a Hindu temple and it flutters on all days. Symbolically, hoisting the flag suggest setting out to conquer, and a devotee comes to the temple to conquer his ego and gain control over the baser nature with the help of the Supreme Being.
Some flags and banners hoisted in temples act as a message board and give an idea about the deity worshipped in the temple. It also suggests which particular incarnation or manifestation of the God is given importance in the temple.
Some temple flags are specifically designed for the purpose of temple festivals and are only hoisted during the festival period.