What are symbols in the story "The Necklace" by Guy de Maupassant?

The borrowed necklace itself is a good symbol because of the fact that it looks beautiful and expensive but is made of false jewels. Mathilde is susceptible to being deceived and misled by meretricious things. She lives in a fantasy world. Losing the borrowed necklace makes her wake up to reality. Maupassant was a realist, like his uncle and mentor Gustav Flaubert. He was also strongly influenced by the German pessimistic philosopher Arthur Schopenhauer, who once wrote:

It is very important for us to learn early in youth that we are living in a masquerade, otherwise we shall be unable to grasp and get at many things but shall stand before them quite puzzled; and indeed those will stand longest who ex meliore luto finxit praecordia Titan. ('Whose heart was fashioned by Titan out of better clay,' Juvenal, Satires, XIII, 183). . . Almost invariably, the genuine article is rejected and the merely spurious sought. And so young men should be taught that in this masquerade the apples are of wax, the flowers of silk, the fish of cardboard, and that everything is a plaything and a jest. 

Part of Mathilde's great social triumph at the Minister of Public Instruction's ball is due to the fact that, like Cinderella in the fairy tale, she makes a great impression with a necklace that is not her own and a gown her husband could barely afford.
The fake necklace also symbolizes youth, grace, charm, and beauty. It is a useless luxury item appropriate to the wastefulness and privilege in the lives of shallow people. Sir Francis wrote in his essay "Of Riches":

Do you not see what feigned prices are set upon little stones and rarities? and what works of ostentation are undertaken, because there might seem to be some use of great riches?