When Pharisees and Sadducees asked Jesus to show them a sign from heaven, He mentioned signs that He had already put in the heavens. But he accused them of being too hypocritical to recognize those signs already given as signs from God.
It is evident from Scripture that God put the red sunset and red sunrise as signs in the heavens pointing to Jesus Christ. Physically we see these as signs for the weather. We say: Red at night, sailors delight; red in the morning, sailors take warning. If we would see them as signs from God, we would say: Red at night, sinners delight; red in the morning, sinners take warning. The slides, Signs in the Sky, document this from verses throughout the Bible and establish how the Pharisees and Sadducees should have been able to recognize this.