Symbolism, Imagery, Allegory
The Bourne Identity is a thumping, thundering, thick adventure novel. It wants to make you turn the pages. It wants to get your adrenaline pumping. It likes guns and sex and shiny plot twists.
All of which is to say: Symbols? Imagery?The Bourne Identity does not care. If you're pausing for a moment to think about what the fishing boat means, or what the deep significance of the elevator button is, then The Bourne Identity feels it's not doing its job. Forget all that! Turn the page, already!
So, does this mean that symbols and imagery are completely absent in The Bourne Identity? Not exactly. Even if you're trying hard to avoid it, it's hard to escape that kind of thing altogether. But the symbols that the novel uses tend to be pretty simple and straightforward. They often function more as shorthand, to telegraph ideas quickly and concisely, rather than to deepen or complicate matters.
For example, Bourne's eyes. Early in the book, Washburn tells Bourne that his eyes are "[h]azel-grey in one light, blue in another" (1.87). In other words, his eyes change color depending on the light and the background. Later in the book, even the love of Bourne's life, Marie St. Jacques, can't tell him what color his eyes are: "I'm not really sure. I suppose that's dreadful of me" (14.27). Moreover, Washburn is able to tell medically that Bourne has worn contacts, though he (naturally) doesn't need them to correct his vision. Bourne's eyes, in other words, are indeterminate, and on top of that, he has deliberately worn contacts to change his already changeable natural attributes.
So what's the symbolism here? Well, Bourne's changeable, chameleonic eyes stand for the changeable, chameleonic Bourne himself. Those hazel/blue/whatever orbs are a quick and dirty way to make the point that Bourne is a super-secret spy who can change his appearance at will, so that even those closest to him can't be sure who he is.
We also noticed that in both instances above—in chapter 1 and chapter 14—the eyes are discussed in the context of exposition. That is, Washburn tells Bourne about his eyes to prove that he's unusual. Then Bourne tells Marie about his eyes in order to prove that he's a sneaky spy. You never actually see the eyes changing yourself. They're symbolic, sure, but even more than that, they're shorthand: they're there to give you information you need in a quick, easy-to-remember way—so you can turn that page, already.