The sign of Jonah is one of those things which looks like a Biblical inconsistency and the various ways that Christian scholars have tried to resolve it are hopelessly contrived. On the face of it, it looks like Jesus lied.
The Sign of Jonah
The Earth with Her Bars
"The earth with her bars" is how Jonah described the pillars of the earth when he was in the belly of hell, possibly in the place which we refer to as Abraham's bosom. Jesus also went here after the crucifixion.