What did Pilate do to symbolize his innocence in Jesus' death?

Answer: Washed his hands

Pilate took water and washed his hands, saying, 'I am innocent of this man's blood.'

“When Pilate saw that he was accomplishing nothing, but that instead a riot was breaking out, he took water and washed his hands before the crowd. “I am innocent of this man’s blood,” he said. “You bear the responsibility.””— Matthew 27:24 (BSB)