I think that one of the most powerful symbols in the story is the window that is in the narrator's room. The windows that "look all ways, and air and sunshine galore" are fundamentally different from the imprisoned condition that the narrator perceives. The window is a symbol of what can be, the freedom and the agency that might await her. The window is symbolic of what the narrator believes will help her in terms of walking, getting out of the house, and being able to be the agent of her own actions.
I think the contrasting symbol to this would have to be the wallpaper itself. The description that the narrator offers of the wallpaper brings out its symbolic condition:
It is dull enough to confuse the eye in following, pronounce enough to constantly irritate and provoke study, and when you follow the lame uncertain curves for a little distance they suddenly commit suicide- plunge off at outrageous angles, destroy themselves in unheard of contradictions.
The "repellent" texture is symbolic of how the husband has taken away any joy and agency in the woman's life, reflecting a world far from a "beautiful place." The wallpaper is symbolic of a constructed world for the narrator, one where there is an absence of "society and stimulus." As a result, the narrator has focused all of her energy on the wallpaper and the designs that enable her to see "perseverance as well as hatred." The world that the narrator sees is not the world outside her window, but rather one within the wallpaper where "dim shapes get clearer every day." It is a symbol that represents the growing chasm between the narrator and reality. It is also a symbol of what happens when thinking energies are suppressed under simplistic notions of what's good. The wallpaper becomes the symbol that reminds the reader of how wrong "the medical profession" was in treating patients, and women, in particular.