Big Boy's decision
When Big Boy decides to strip naked with his buddies and go skinny dipping as they had planned, he does so despite a white man trying to intimidate them into leaving. Ultimately, he finds out that his friends' lives are at stake, but his decision actually represents a kind of justice. It's his way of saying that on God's earth, all the animals are welcome. This is symbolized by their nakedness, as if they were just another breed animal making use of a natural body of water. In other words, the White man's decision to harass them is an attempt to tell the Black kids that they are not even allowed in nature. Therefore, Big Boy's decision is heroic, because who is that random white guy to tell them that their lives don't even belong in nature?
Bob's betrayal
There is a horrendous betrayal in the story Down by the Riverside that ends up with the whole family dying. Bob is given a donkey to sell so he can purchase a boat so his cousin Mann can take his wife to the hospital, because she's dying of labor complications. But instead, Bob spends the money, steals a boat, and gets them all killed. This is a symbol representing the damage criminals inflict on their community. By being evil, they make everyone's impression of Black people even more judgmental and unfair.
The symbolic betrayal of Sarah
Now, he's another betrayal. It seems husbands can betray their wives by taking her suffering and playing the victim about it. That would hypothetically work backward as well, but in Long Black Song, Sarah is a literal rape victim. When her husband returns (whom she desperately loves and misses), he treats her like the villain, and he plays the victim and beats her. So not only is she raped, but her husband betrays her. He murders the man and gets himself killed, which leave Sarah and the Baby alone in the wilderness, another sign of betrayal.
The martyrdom of suffering
Preacher Taylor learns a lesson the hard way in Fire and Cloud. The beginning of the story is basically him trying to find the courage and strategy it would take to bring some real social change, but no one will help him, although some people lie to him and pretend they will help him. He is smart, so he sees through that, but he also sees something else—when he is beaten randomly by racists, he finds his courage. Having witnessed the pure terror of racism, he is now ready to face the challenges ahead of him, out of love for his community.
Communism as a motif
If Communism is a symbol in this book (it would be difficult to argue that it isn't one), then the motif of the white Communists refusing to help Black people is a symbol for racism, because only racism would prevent a utopic person from realizing that, if one people group is complete subjugated to another by socioeconomic manipulation (AKA Jim Crow), then how could the theory of Communism be tenable? If Black people aren't viewed as people, then the Communists feel no loyalty to extend their generous liberal philosophies to them. This symbolizes the ubiquity of racism.