Symbolism, Imagery, Allegory
The family car makes for an interesting symbol because it is intended to mean one thing but works out to mean another: James buys the thing as proof of how much he cares for Mary. He also wants to show the whole neighborhood that, while he is frugal, he has good taste and knows how to spend. Unfortunately, the car he buys is a lemon that James picked up used. Mary just sees it as a symbol of her husband's thoughtlessness, long absences, and miserly ways.