There are a number of instances of symbolism in Emperor Jones. The examples of symbolism function on varying levels of significance, from visual representations of Jones' mental state to deeper symbols that represent broad psychological ideas to conventional symbols of social institutions and social practices.
To start with the most immediate symbols in the play, we might look at the clothes Jones wears. His clothes are torn to shreds as he makes his way through the forest at night. He also takes his shirt and shoes off. These details reflect the character's increasing exposure to (1) his sense of paranoia and fear and (2) an implied descent into the forces of guilt and trauma that characterize his unconscious mind (and his past).
The drum sound can also be read symbolically, to some extent, as it represents the irrepressible power of the psyche (associated in the play with the natives, their unwavering resolve and their magic).
The forest itself is a symbol in the play as it represents Jones' unconscious mind and/or suppressed guilt. In the forest, Jones is forced to face his fears, meeting the ghosts of men he has killed and also encountering scenes of a collective past that haunt him as a black man.
"And as Jones re-enacts in the forest the horrors of the slave trade that brought Africans to America, O’Neill’s implication is that Jones is also a victim of American racism" (eNotes).
The pulpit, the auction block and the slave ship are each discovered in the forest as aspects of a collective history that informs the sum character of the protagonist (as a man of a particular race with a particular history of violence, exploitation and dis-empowerment). Each of these facets of black history in the Americas can be read as a symbol, representing the social institutions of church and commerce that facilitated the creation of a black underclass.
There is a strong suggestion of the forest's symbolic significance in the fact that Jones cannot escape these specters of the past and that he also becomes lost in the forest, returning to where he began. The forest is a place of no escape. It is, instead, a place of confrontations between Jones and his past, his mind and the fears that populate each.
"At the end of the play Smithers says of Jones, ‘he’d lost ’imself,' and Jones is indeed a man in conflict with his past and the self he created to hide from it" (eNotes).