no sign will be given , page-13

Despite all of Jesus’ powerful works, the scribes and Pharisees request: “Teacher, we want to see a sign from you.” Although these particular men from Jerusalem may not personally have seen his miracles, irrefutable eyewitness evidence regarding them exists. So Jesus tells the Jewish leaders: “A wicked and adulterous generation keeps on seeking for a sign, but no sign will be given it except the sign of Jonah the prophet.”

After being swallowed by the fish, Jonah came out as if resurrected, so Jesus is foretelling that he will die and on the third day will be raised alive. Yet, the Jewish leaders, even when Jesus later is resurrected, reject “the sign of Jonah.”
Is it any different today? Many demand proof before they will believe. Abundant proof already exists. Therefore no sign will be given except the "sign of the Son of man." Matthew 24:30.