What metaphors are used in Recitatif by Toni Morrison?

At one point Twyla comments on her protest sign slogan, admitting that "actually my sign didn't make sense without Roberta's." This may be understood as a metaphor for the idea of difference that Morrison expresses in the story. The signs or codes used to suggest Twyla's race don't make sense without an opposing set of signs or codes that define Roberta in contrast.