The quote to which you are referring actually occurs in Chapter 21 of To Kill a Mockingbird. Tom Robinson had just been declared guilty by the all-white jury, and Atticus was on his way out of the courtroom. After nodding to the prosecutor, Horace Gilmer, he put his hand on Tom's shoulder and whispered something to him. Then he pulled his coat over his shoulder and headed the short way out of the room. He did not look up at Scout and Jem, but Scout felt someone punching her. She noticed that all of the black people in the balcony were standing, and Reverend Sykes said to her:

"Miss Jean Louise, stand up. Your father's passin'."

By standing, Tom's supporters were showing their respect for Atticus' staunch defense in a trial he could not win.