What is an example of symbolism in the novel, A World of Curiosities?

The thin iron ring is a symbol of identity and disaster. These iron rings are given to graduates of the École Polytechnique. Connor McNee, one of Fleming’s victims, was an engineer who had one of these rings. Gamache discovered the ring in front of the door to his safe room where he stored his private files. When he learned the identity of the last person who wore the ring, he realized that Fleming had it planted there as a message to Gamache.

The rings are also symbols of the disasters that can happen as a result of mistakes in engineering. They are made from debris from the first Québec Bridge, a bridge that collapsed while being built killing 86 people.