Three symbols in Sing, Unburied, Sing include Parchman Farm, the gris-gris bag, and vomiting.
Parchman Farm, or the Mississippi State Penitentiary, is a symbol of the trauma of racial injustice that impacts so many in the novel, including Pop, Jojo, Richie, Bishop, Stag, and Michael. All of them serve time in this heavily and disproportionately Black penitentiary, and all are marked by the psychologically damaging experience. As the novel points out, Parchman's is a continuation of the horrors of slavery. Even calling it a "farm" links it to the farms and plantations that were once, in fact, prisons for the slaves.
The gris-gris bag that Jojo finds stashed by his grandparents amid his belongings as he goes to Parchman is a symbol of good luck. The bag represents his ancestors and their love and protection. Even though they can't be with him, the voodoo amulet they pack shows Jojo that his family is with him in spirit. This African artifact symbolizes, too, that the Black community finds a sense of safety in their own heritage rather than in the dominant white society.
Vomiting in the novel is a symbol of Black characters trying to rid themselves of what is destructive to them in white society, such as when Leonie vomits up meth.