There will be no other sign given except Jesus' own death and resurrection which echoes Jonah's experience. He said this Himself. So then if people are looking for other signs, doesn't it demonstrate a lack of understanding of the Master's words?

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The Sign of Jonah

38 Then some of the scribes and Pharisees told Jesus, “Teacher, we want to see a sign from you.”

39 But he replied to them, “An evil and adulterous generation craves a sign. Yet no sign will be given to it except the sign of the prophet Jonah, 40 because just as Jonah was in the stomach of the sea creature for three days and three nights, so the Son of Man will be in the heart of the earth for three days and three nights. 41 The men of Nineveh will stand up at the judgment and condemn the people living today, because they repented at the preaching of Jonah. But look—something greater than Jonah is here! 42 The queen of the south will stand up and condemn the people living today, because she came from so far away to hear the wisdom of Solomon. But look! Something greater than Solomon is here!”

(Matthew 12:38-42)