There aren't too many symbols or even images in this story. After all, it's nearly all dialogue between two people—and they're not exactly speaking in poetic, Shakespearian language that's dripping with metaphors. But, at the very beginning, when the narrator is setting up the situation, we get a brief piece description, which includes images that hint at a deeper meaning:
She had been staring raptly out of the window, drinking in the big weathered signboards that extolled the phenomena of codfish without bones and screens no rust could corrupt. (4)
While her husband finishes packing, the wife gazes at the scenery in distraction. The "phenomena" advertised by the billboards—boneless cod and rust-less screens—are images of innocence.
The rust-less screen is one that is described to be "uncorrupted," language that mimics the very 1930s understanding that sex "corrupted" young women and left them less-than-wholesome. Also, to delve deeper, a screen is something that protects an opening (a window or door) from unwanted intrusion. It's not as impenetrable as a door—you can tear a screen, especially if it's weakened by lust, erm, we mean rust—but it still offers some protection.
Huh. You know what else protects an opening, but can be easily rent? A hymen.
More scandalous still is the image of the cod. A (kind of icky) comparison is often made between fish and vaginas—just think of the term "fish taco" and the vaginal association often given to oysters. And this particular kind of fish is "boneless." Yup. That's a virgin fish, folks. No phallic bone in this fish—not yet, at least.
Recap: Parker is implying that the wife is contemplating her virginity as she looks out the window, wishing it farewell, before turning to the future, represented by her husband.