Describe symbolism in Tears of the Giraffe by Alexander McCall Smith

In Chapter Five, Mr. J.L.B. Matekoni finds that Mma Ramotswe does want a diamond engagement ring. They talk about how there are no secrets in Garborone and how everyone's secrets are known. They both appreciate the value of confidentiality. She mentions that people have been asking to see her engagement ring. Mma Ramotswe explains that the diamond ring is a symbol of appreciation and that there are inexpensive diamonds.