This is an ucu, more recently called a beaded love letter. In the book, Sindi's lost ucu helps the Zulu prince to find her!
Before the days of mailing letters, Zulu women could use beadwork to send a message to a loved one. Married women would send them to their husbands and maidens would send to suitors as symbols of their love and affection. While some symbols and colors formed a easily understood message, others created a message known only to the couple.