Sunflower Symbol
The sunflower is a symbol of remembrance in the book; as he is going to the hospital from the camp, Simon is taken past a cemetery and sees that each gravestone has a sunflower on top of it in an act of honor and remembrance for each German soldier buried there. This also makes him fear that he will receive no remembrance at all and that he will be thrown into a mass grave with thousands of others. The sight of the sunflower symbolizes remembrance and honoring the dead to Simon.
"Forgive and Forget" Symbol
It is revealed in the book that the majority of Germans are of the "forgive and forget" mindset, meaning that they feel the Jews should forgive, forget and move on. This is a symbol of the German's wish to move on from their actions - an inactions - during the Holocaust and in some way absolve themselves of any responsibility for their role in it.
Coffee Symbol
Simon describes the dark liquid said to be coffee that was given to prisoners each morning. Although he did not always drink this, his friend always did, because drinking coffee at breakfast was a symbol of normalcy; it symbolized the start of the day, the beginning of work, and the way that things were before the persecution that led him to the prison camp.
Karl's Mother Symbol
Karl's mother was not a Nazi - in fact, she had been vehemently opposed to her son joining them. She maintained to Simon that she had no part in the atrocities, and that she held no bad feelings towards the Jews, with whom she had existed happily and peacefully before the war. She is a symbol of all of the German people who believe they had no involvement in the atrocities committed in the war, because she does not see her silence as complicity.
Simon Swatting a Fly Symbol
While he is sitting at Karl's bedside and hearing his story, Simon swats a fly away from him as one would do for any other human in his position. He also holds his hand to calm him as he talks. These simple, decent acts are a symbol of Simon's compassion as a human being and for his humanity towards others, even when he is being de-humanized himself.
