Return Customer
Lincoln gets a return visit from a man each week, but he can't see his face, only a distorted reflection of his face in nearby electrical box. The man always says something deep to Lincoln. The man is a symbol of Lincoln's looming death and the distorted reflection represents the fact that he won't know who will kill him.
Inheritance
Booth has kept his $500 inheritance from his mother for years, and has never touched it. It is a symbol of Booth holding on to his mother coming back to him, that he hasn't given up hope.
Lincoln
Lincoln was named by his father who thought it would be ironic, and wanted to see how it played out. His name becomes a symbol of his doomed fate.
Booth
Booth, like his brother was name by his father. His name is a symbol of him becoming a killer, thus being the dangerous one of the brothers.
Grace
Grace is the woman who Booth is in love with. He wants her to take him back so they can spend their lives together. Her name represents the grace that he needs in order to be saved from his reckless ways, a grace which he does not receive.