Symbols

The Cleft lip

In the Kite Runner, the cleft lip is a symbol of social status in the Afghan society. Those with cleft lips usually live in poverty because they cannot afford surgery to fix it. Amir describes Hassan as "the harelipped kite runner." page 2.  Hassan’s cleft lip marked his status as a Hazara, which divides him from Amir who is a Pashtun. When Baba fixes Hassan’s lip as a birthday present which symbolized Hassan being freed of his physical label and also Baba's secret love for Hassan.

The Kite 

To Amir, the kite is a symbol of childhood. The book starts off in San Francisco where Amir is living comfortably as a grown man. He sees kites flying in the park and is reminded of his childhood in Kabul, flying kites in competitions. However, the kite is also a symbol for guilt. After winning the kite cutting tournament, Amir finds Hassan with the kite surrounded by Assef in an alleyway. Amir watched Hassan get raped by Assef but cowardly runs away instead of standing up for his friend. Hassan being the loyal servant he was, brought the kite back to Amir even though he sacrificed himself and lost his dignity in the process. As Amir grows older, the guilt continues to plague him. Even in America when he marries Soraya but cannot have children because of unexplained infertility, Amir believes that it is a form of punishment for his betrayal to Hassan. The kite is also the only thing connecting Amir and his father. "Baba and I lived in the same house, but in different spheres of existence. Kites were the one paper-thin slice of intersection between those spheres."page 52. Amir is very different from his father in terms of character and interests, the kite is the bond and common ground they have a father and son. 
At the end of the book, the kite no longer holds guilt behind it because Amir has been redeemed of his past. It symbolizes the childhood memories with Hassan.

“I ran. A grown man running with a swarm of screaming children. But I didn't care. I ran with the wind blowing in my face, and a smile as wide as the Valley of Panjsher on my lip. 
I ran” page 391.

Amir’s scar

Amir gets a scar above his lip from Assef while fighting to rescue Sohrab. He now shares the same permanent scar that Hassan has above his lip from the surgery. The scar symbolizes their brotherhood as they are born from the same father. Amir’s scar also represents courage because he finally stood up for those he cares about. Amir’s character had changed from a cowardly boy into a brave honorable man who would have made Baba proud.

“The impact had cut your upper lip in two, clean down the middle. But not to worry, the plastic guys sewed it back together and they think you will have an excellent result, though there will be a scar.  That is unavoidable.” page 311.