Symbolism in catching fire
The Mockingjay
The stunt that Katniss pulled with the berries was the main event that got Katniss to be the symbol of the rebellion. Because she wore the Mockingjay pin, that became her symbol. The came to view Katniss as the Mockingjay. The looked at Katniss to be the symbol of rebellion which caused the Mockingjay on her pin to symbolize it.
Three finger salute
The three finger salute is what the citizens of District 12 do to show respect. It's not done a lot, only when something major happens and to someone that deserves it. It was first done in The Hunger Games when Katniss volunteers to go into the games for her sister. In Catching Fire the people of District 11 did it to show respect for Katniss because of the how she put flowers around Rue's body when she died. It shows respect but when they did it it also implied that they would stand behind her.
Rue
Rue is not alive in this book but she is mentioned because of her impact in the last book. She is a small girl that was forced to go into the Hunger Games. She symbolizes innocence and how evil the games are because they send innocent people into an area to be tortured and brutally killed.