What object serves as a symbol of honor in the novel, The War That Saved My Life?

After the man that Ada sees rowing to the ocean shore is determined to be a spy, the policeman who didn’t believe Ada's story comes to apologize to her. He brings her the gift of an onion. This onion is significant because imported onions were very scarce and the residents of Kent had not yet had time to grow onions in their victory gardens. As a result, the onion becomes a symbol of honor.