Symbolism, Imagery, Allegory
Everyone likes to have a little bling—even Shakespeare's characters. When Imogen and Posthumus say goodbye to one another, they give each other jewelry. Even though these are just little items, they carry huge significance in the play—Imogen and Posthumus aren't just into jewelry: these are love tokens, or signs that show that the two of them are together. Elizabethans used love tokens to tell everyone around "she's mine" and "he's mine."
What's the big deal about these love tokens? Well, Imogen's ring used to belong to her mother, so it's important to her even before she gives it to Posthumus. Posthumus calls the bracelet a "manacle of love" (1.1.143), and he later refers to "my ring I hold dear as my finger" (1.4.141). So far, so good.
Things quickly go awry when Posthumus bets the ring in his wager with Iachimo (why, Posthumus? why?). We know that Iachimo gets the ring and bracelet before too long, but we think it's interesting what he does with them. He tells Posthumus, "I beg but leave to air this jewel. See— / And now 'tis up again. It must be married to that your diamond" (2.4.121-123). It's as if the jewels are intertwined in some way—or "married," as Iachimo puts it.
Even Iachimo gets the symbolic value of these jewels: they're not just precious because of their monetary value—they've become symbols of the love and trust Posthumus and Imogen share (or think they share). That's why Iachimo thinks it's so important to steal Imogen's bracelet as proof that he hooked up with her: it's not just a sign that he was with her—it's also a sign that he has taken away that love and trust.
What's surprising is how easy it is for Iachimo to get it. When he's removing the bracelet from Imogen's arm, he says: "Come off, come off; / As slippery as the Gordian knot was hard!" (2.2.37-38). Seriously: it just slips right off like it's nothing. Does Posthumus consider that Iachimo may have just stolen the bracelet from Imogen? Nope. He's too invested in that bracelet to consider any possibility but the worst.
If you've read Othello, you know that Shakespeare's jealous husbands can be tricked pretty easily by small trinkets like bracelets and handkerchiefs.
In the end, it's the jewelry that saves the day. When Imogen sees her husband's ring on Iachimo's finger, she questions him about it… and this time, he unravels the entire plot. The truth has a nice ring to it.
Think about how close this story came to becoming a tragedy, folks. It came really close… and all over a little bracelet.