Jonah himself wasn’t much of a sign, if you think about him. He fled fear-stricken from the mission God gave to preach to the great city of Nineveh, and when the sailors on the boat from Joppa saw him as the curse that caused a storm and threw him overboard to drown, he couldn’t stop them. That would have been the end of him if God didn’t send a whale to swallow him and vomit him up on the shore at Nineveh.
An arrival like that caught the attention of the Ninevites; they listened to this man who came from the belly of whale and responded to his preaching by begging God for forgiveness.
So Jonah wasn’t much of a sign himself. The Ninevites would have ignored him if he just got off the boat from Joppa and preached to them. Instead, he was someone brought back from death and sure destruction. God made him a sign of life.
In Jesus, a greater than Jonah is here. The mystery of his death and resurrection is at the heart of his mission, his great word, his message of hope, his sign of love for us.
The Sign of Jonah was a favorite theme early Christians used to decorate the places where they buried their death. The whale of death, monster of the sea, would not destroy humanity but deliver it to another shore, where a kingdom was waiting.