The most dominant symbol in the play is the handkerchief that circulates throughout the play. Because Othello gave it to Desdemona as a first gift, the handkerchief functions as a token of his love, which Desdemona cherishes. This is why Iago convinces his wife to steal it from Desdemona – he knows that it has a lot of sentimental value and that Othello will be angry when he finds out his wife no longer has it.
Iago also knows that, for Othello, the handkerchief symbolizes Desdemona's fidelity. When it shows up in Cassio's possession, Othello is convinced that Desdemona is unfaithful. The white napkin, as we know, is spotted with red strawberries and Othello tells Desdemona that the strawberries were hand stitched with thread that has been dyed with blood from "maidens' hearts" or, virgins' blood. In this way, the handkerchief resembles a white wedding sheet that's also been stained with a virgin's blood. So, in Othello's mind, as long as Desdemona has the handkerchief in her possession, she's chaste. But, the moment she "loses it," she looses her chastity.
The handkerchief also seems to function as a symbol of Othello's mysterious past and his "exoticness." He tells Desdemona that an Egyptian "charmer" gave it to his mother and that it would keep his father "faithful" and under her spell. That such a small object has such enormous weight in the play testifies to the sensitivity of jealous minds, and the way that small incidents can be magnified psychologically into "proofs" of love or betrayal.
You've probably noticed how the word "honest" shows up all over the place in Othello. By poet and literary critic William Empson's count, there are 52 uses of "honest" and "honesty" throughout the play. Like the word "nothing" in King Lear, "honest" has a wide range of meaning in Othello. At times, it refers to chastity, the question of whether a woman is "honest" or whether she is promiscuous. At other times, the word refers to personal honesty, whether or not a person is telling the truth. It can also refer to whether or not a person is a good and loving friend.
These meanings come together in some ironic ways throughout the play. The clearest example of this is how Iago uses personal dishonesty (lies and deceit) to convince Othello that his wife is sexually dishonest (cheating on her husband), all while pretending to be looking out for the best interests of his so-called friend.
Every major character in Othello packs up and heads for Cyprus, where we've been promised a bloody battle. And then, due to inclement weather, there is no war. We, the innocent and unknowing reader, accept this with a little confusion and move right onto the sordid plot.
We might forget about the whole war thing until Othello's crucial monologue in Act 3, Scene 3, in which he describes the components of the battlefield - horses, troops, trumpets, banners, canons - and how they are all lost to him now that he knows Desdemona is unfaithful. Here, these implements of war become symbols of Othello's sexuality. Think about it - what's more manly than a big collection of war-like objects? Desdemona has deflated him; he is un-manned by her betrayal.
So what's the conclusion? We got our war in Cyprus, after all; it's just that the battlefield turned out to be the mind, not the literal battlefield. If all is fair in love and war, then it's a bloody battle indeed going on in Othello's psyche.
The Willow Song
As Desdemona is preparing for bed the night she is murdered, she starts singing a song about Willow trees. This song, supposedly sung by one of Desdemona's mother's servants who loved a crazy person, reflects Desdemona's own situation. She herself is worried that the man she married has gone crazy and will desert her. Willows at the edge of the water are a traditional symbol of women who are deserted by their lovers.
Cassio's Naughty Dream
When Othello asks for "living reason" (proof) that Desdemona's been "disloyal," Iago tells him about a **** dream that Cassio supposedly had one night while he was lying in bed next to Iago (presumably, at an army camp). According to Iago, Cassio talked in his sleep while dreaming about a steamy encounter with Desdemona. Not only that, but Cassio also grabbed Iago, wrapped his leg over his thigh, and made out with him, all while dreaming about Desdemona, of course.
What's going on here? First, it's important to note that Iago is framing Cassio to make it look like he's sleeping with Desdemona. Second, Othello seems willing to accept this graphic story as "proof" that Desdemona's cheating. Third, Iago is describing a blatantly homoerotic moment he has allegedly shared with Cassio. The description of the dream is supposed to be about Desdemona and Cassio, but that becomes less important than the graphic description of what goes down between Cassio and Iago, which begs the following question: Is Othello upset/jealous that Cassio (allegedly) had dream about his wife, or that Cassio was lying in bed and groping Iago? Literary critics have argued both ways, so take your pick.
The candle that Othello blows out just before he strangles Desdemona symbolizes Desdemona's fragile life. Othello draws the comparison himself - as he stands over a sleeping Desdemona with a lit candle in his hand, he says he's going to 'put out the light, and then put out the light' (blow out the candle and then strangle Desdemona). He also muses that the difference between Desdemona's life and a candle's light is that he can put out and relight the candle over and over if he so chooses, but he can kill Desdemona only once: 'If I quench thee, thou flaming minister, / I can again thy former light restore, / should I repent thee' he says to the candle. 'But,' he says to the sleeping Desdemona, 'once put out thy light, / Thou cunning'st pattern of excelling nature, / I know not where is that Promethean heat, / That can thy light relume'.