What are some race-related events that are foreshadowed throughout Harper Lee's To Kill a Mockingbird and really remind the reader the underbelly of racism in America is never far away?

One race-related event in Harper Lee's To Kill a Mockingbird is the outcome of Tom Robinson's trial. Robinson's innocence in the crime he's being accused of is made evident the moment during the trial we learn that Mayella Ewell had been bruised on the right side of her face, which could only have been accomplished by a left-handed man facing her, whereas Robinson has been crippled in his left arm and hand since he was a boy and got his arm caught in a cotton gin. What also convinces the reader of Robinson's innocence is the fact that Atticus proves to the court that Bob Ewell is ambidextrous. Since Robinson is innocent, it is clear he has been brought to trial and declared guilty by the jury simply because of the color of his skin.Robinson's guilty verdict, despite his innocence, is foreshadowed in the book's title and the scene in which the meaning of the title is explained to the reader. In Chapter 9, Scout and Jem are given air rifles for Christmas. In Chapter 10, Atticus expresses his wish that Scout and Jem would only shoot "tin cans in the back yard" but, knowing they'll shoot birds, gives the the following warning:

Shoot all the bluejays you want, if you can hit 'em, but remember it's a sin to kill a mockingbird (Chapter 10).

When asked, Miss Maudie explains to Scout that Atticus is correct in saying the above because mockingbirds don't cause mischief like other birds; all they do is "sing their hearts out" all day long (Chapter 10). Therefore, the mockingbird symbolizes all innocent beings in the story, such as Robinson, and Atticus's warning not to kill them foreshadows Robinson's defeat in his trial despite his innocence, a defeat incited by racial hatred.In this same chapter, the death of the rabid dog named Tim Johnson foreshadows Robinson's death after his trial, a second race-related event. Though Robinson would be on death row for quite a while and Atticus had hoped to overturn his sentence—possibly even his conviction, upon appeal—Robinson gave up all hope of being served justice by white men and, immediately after his trial, decided to try to take justice into his own hands by attempting to escape prison. He was shot to death while trying to escape and shot far more times than really necessary, which shows he was shot and killed out of racial hatred, not out of the guards' necessity. Just as Robinson was shot to death as an innocent man, Tim Johnson was shot to death as a helpless, innocent dog. Dogs certainly don't become infected with rabies intentionally, nor do they mean to cause the harm and death they can cause once infected; therefore, Tim Johnson, though rabid, also symbolizes an innocent being, a being society thinks must be killed because the being has become violated by something evil, something like racism. The death of Tim Johnson foreshadows Robinson's upcoming death. We especially see what Tim Johnson's death foreshadows when Scout remembers his death just after the lynch mob scene. In bed that night, Scout reflects in her narration:

I was very tired, and was drifting into sleep when the memory of Atticus calmly folding his newspaper and pushing back his hat became Atticus standing in the middle of an empty waiting street, pushing up his glasses. The full meaning of the night's events hit me and I began crying (Chapter 16).

Standing, waiting, and pushing up his glasses in the middle of a street is exactly what Atticus did while waiting with Sheriff Tate for Tim Johnson to come within shooting distance. If Scout associates shooting Tim Johnson with Atticus guarding Robinson from a lynch mob, then we know Scout has realized the death of an innocent being is about to take place a second time, and Atticus is doing his best to prevent it, despite its inevitability, just as he at first refused to shoot Tim Johnson.