Its always a little fun when Jesus gets testy with people. Don’t you wish you could hear the tone he really used with the Pharisees?
Jesus was accusing them of knowing full well who He was, but intentionally seeking to turn the people against Him. That would be the worst offense possible, so their response to him was, “prove it.” At that point Jesus seems to be saying: ummm… where have you been? If you want a sign, you’ll get a sign (but by then it will be too late).
The Jonah reference is two-fold, the obvious is that He points to His own resurrection, but the second is one of judgment. The Ninevites repented after Jonah, but about 40 years later the city was sacked and destroyed. About 40 years after this conversation between Jesus and the Pharisees, Jerusalem and the temple would be destroyed by the Romans.
Don’t deny the Holy Spirit when you see it working and when you call out to God looking for a sign, be aware that He will often trigger memories of past times when He’s worked in your life. One of the reasons that we are encouraged to be in community and in small groups, is so that we can share our “signs” with one another.
How often have you wanted a sign and immediately God brought a memory of a time when you knew His presence, or the story of someone that has always brought you God’s peace?