What happened with Jonah?
As the crowds were increasing, He began saying: “This generation is an evil generation. It demands a sign, but no sign will be given to it except the sign of Jonah. For just as Jonah became a sign to the people of Nineveh, so also the Son of Man will be to this generation.”
After Jesus was resurrected, Thomas, a disciple, said that he would not believe his friends, that Jesus had been resurrected, unless he saw Christ in person (John 20:24-25). So when Jesus showed up, Jesus said to Thomas, “Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe.” (John 20:27)
Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed”. (John 20:29)
A lot of people will say that they would believe in Jesus if they could see a definite sign or a miracle. We have all the proof we need in the words of the Bible, and the testimony of the those who saw what Christ did when He was here as a man. It does take a measure of faith, and God can definitely help with this, you only need to ask!
For we also have had the gospel preached to us, just as they (the Israelites) did; but the message they heard was of no value to them, because those who heard did not combine it with faith. (Hebrews 4:2)
We will receive no further signs. Stop doubting and believe.