This section is tough for "The Murders in the Rue Morgue," and for an interesting reason. There are a lot of things in this story: gold Napoleons, dresses in a bureau, paving stones, bodiless images of the Goddess Laverna. And so you might think that there would be an equal number of symbols, where a symbol is a physical object or character that represents an abstract idea. With so many objects to choose from, one of them has to say something meaningful.
On the other hand, Poe is tricky. He's writing a new kind of story, a "tale of ratiocination" (check out "In a Nutshell" for more), in which he's making a literary text into a puzzle. And we don't usually look at puzzle pieces for their symbolic value. That's not to say that the objects in "The Murders in the Rue Morgue" have no meaning, but that significance is not abstract at all. Objects (and even people; the sailor is just more proof, in a sense) constitute evidence.
We think, when we first read this story, that the four thousand francs might represent something, like the motive of the killer. But we learn that this is a red herring, and that they are coincidental. There is no hidden meaning, and we can discard them. Similarly, we might not initially make anything out of the shrill, unequal voice with no words. However, by the end, we realize that this is one of the best bits of proof Dupin has that the murderer is a giant ape. For all of the detail in the story, none of it is abstract: it all comes under the heading of either "important evidence" or "not important – ignore."
The biggest symbols in the story take the form of people. Dupin stands as a representative of the whist player's imaginative and rational mind, the Prefect of Police is a model of the chess player's analytic mind, and our friend the Ourang-Outang represents irrational emotion. But we've already gone over this: check out our "Character Analyses" for more on what the characters themselves might symbolize.