What was the sign of Jonah?
The Son of Man...dead in the ground(whose in his soul/spirit preached to the spirits in chains in hell proving that he was the Christ during that period)three days and three nights before The Father raised him bodily up again...
That was the sign that was to be given to “this generation”...that is the generation of Hebrews/Jews of Jesus’ time on the earth and then ongoing for the rest of us until he should come again.
The Lord, in order to bring Jonah into a more full accord caused Jonah to have great dis-”gourd” for his attitude towards the Ninevites was most untoward....
The sign of Jonah was a prophecy that Jesus would be in the earth for three days and then raise up out of it.