Why is the Mockingjay the symbol of the revolution?

The mockingjay was chosen as a symbol for the revolution because Katniss wore the mockingjay pin into the arena. Katniss is a symbol of the revolution..... her pin becomes the physical symbol.

My bird has been replicated on belt buckles, embroidered into silk lapels, even tattooed in intimate places. Everyone wants to wear the winner's token. I can only imagine how nuts that makes President Snow. But what can he do? The Games were such a hit here, where the berries were only a symbol of a desperate girl trying to save her lover.