What are the most important symbols in The Hunchback of Notre Dame?

There are, of course, many symbols in Hugo's novels, but two of the most important are the Notre Dame Cathedral and Esmeralda's red baby shoes.

The cathedral serves as a symbol of France, specifically, it represents the possibility of a return to France's former glory. 

Esmeralda's red shoes are a symbol of innocence and purity.  Recall that Esmeralda was kidnapped by gypsies when she was a child.  Her mother managed to save one of her baby's red shoes.  Years later, young Esmeralda meets with a gypsy who has the mate to her baby shoe.  The gypsy tells Esmeralda that as long as she remains virtuous, that one day, she and her mother will be reunited.