I feel that another significant symbol in this play is Portia's ring. Although it is not mentioned in the symbols as given above, it is definitely an important symbol. A ring was given to Bassanio by Portia in Act III, Scene II, when Bassanio passes the casket test and is authorized to marry her. Portia gives Bassanio a ring stating that this ring signified their love and that she is handing over herself and her worldly possessions to Bassanio when she gave him that ring. However she lays the condition that the day that he loses, sells or gives away the ring, Portia would have the right to be angry with him. This ring is essentially a modern day 'engagement ring'.
"Myself and what is mine to you and yours
Is now converted: but now I was the lord
Of this fair mansion, master of my servants,
Queen o'er myself: and even now, but now,
This house, these servants and this same myself
Are yours, my lord: I give them with this ring;
Which when you part from, lose, or give away,
Let it presage the ruin of your love
And be my vantage to exclaim on you."
This is a big deal considering that the play takes place in a time where wives were considered the property of their husbands. Bassanio responds by receiving this ring and saying that the day he parted with this ring, Portia could be sure that he was dead.
"when this ring parts from this finger, then parts life from hence"
At the end of the play, Portia tests Bassanio's allegiance and love for her as well as his honesty and the value of his promises. She demands the ring from Bassanio dressed as a young male lawyer who saves Antonio's life. She is initially pleased that Bassanio refuses to part with this ring, but his true colors are revealed when he sends the ring after her with Gratiano. Portia realizes that Bassanio is not a man of his word. Also, we realize that the bond between Bassanio and Antonio is far stronger than any other relationship in the play. Bassanio shows how he will do anything for Antonio, despite his wife's wishes.
Our doubts about Bassanio's loyalty for Portia is also confirmed. Right from the beginning of the play, we doubt whether Bassanio really loves Portia. He seems to be marrying Portia, a wealthy heiress, only to use her wealth to clear his debts. He even asks Antonio in Act I, Scene I, when he borrows money from him, to think of this money he is lending him as an investment, implying that his primary objective of traveling to Belmont is to gain Portia's wealth.
Hence, I believe that Portia's ring is an extremely important symbol in the play as it displays Bassanio's true character.