I have heard teaching that the sign of Jonah was the resurrection of Jesus after three days.

Jonah was in the whale three days and was resurrected and thrown onto the beach,
where the Ninevites believed in a "fish god" and thought that this was a sign that they
should pay attention to what Jonah said.  What Jonah said was "repent", as your
demise comes in forty days.    Jonah did not expect them to repent, but the Lord God
has instructed him to warn them of this.

In answer to your query about teachings relating this to "now", some have thought
that there would be a resurrection of the Dead in Christ on First Fruits, which comes
right after Passover in the Spring.  They have taught that this would be a "sign" to
the Jews, especially in the Holy Land, that they should accept Jesus as Christ.
They have taught that the risen ones would tell others that Jesus is the Christ.
Sal Smario of Daniel's Glasses has been teaching this for many years, and others
have also taught this.  Sal has expected that the actual rapture would take place
forty days after the resurrection.  The risen ones would testify for forty days before
the rapture.

Others would say that the Sign of Jonah has already taken place:  i.e., Jesus'
resurrection, along with others who rose at that time, and their testimony to the Jews
in Jerusalem which brought about readiness for Pentecost.  So the question
might be, could this happen again, or has the "shadow" of Jonah's resurrection
already been fulfilled in Jesus' resurrection?  Sal Smario says that the sign
of Jonah can come yet another time.

The Apostle Paul taught that the Dead in Christ would rise first, and then those in Christ
who still lived would be raptured.  He did not give a time between resurrection
and rapture.  Forty days of testimony and repentance, followed by deliverance,
is therefore only taught in the Book of Jonah.  Or does somebody know of another
"shadow" similar to this?