"An evil and adulterous generation seeks after a sign, and no sign will be given to it except the sign of the prophet Jonah. For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth." - Jesus, Matthew 12:39-40
When you have a literal miracle worker running around fulfilling prophecy and doing the impossible, it seems a little foolish to demand more proof that He is the God He says He is. He heals people, He raises the dead, He walks on water, He feeds crowds with a picnic basket, and you say "give us a sign", Jesus is well within His rights to be a little bit cross at this request. Nevertheless, He did comply. He offered one sign. He calls it the "sign of Jonah". He predicted both His death and His resurrection, and that prediction came true.
Successive generations have been no less stubborn. "Give us a sign", they say. Some atheists even say they'll believe if He just shows up in front of them. But to those people, Jesus says "I give you the sign of Jonah." Jesus died, was laid in a tomb, and on the third day He rose again.
Given that He is literally offering us the gift of rising along with Him and inheriting eternal life in His Kingdom, as opposed to the eternal wrath we are owed due to our sin, I'd say it's a little bit cheeky to ask for any sign beyond what we already have. How much more evidence should one need to be convinced to take Him up on that? He fulfilled prophecy, He healed the sick, He broke physics, He rebuked the weather, we don't need anything else! But indeed, it is a sign.
There are entire books dedicated to the resurrection. It is a fact of history, as sure as any other. Who else has such power over death but God? The debate is settled. Jesus crushed the devil. The question is, on which side of that victory will you be when you're called before His throne? Will you die in your sins and receive, for all eternity, the wrath due to you, or will you rise with Him in eternal glory, victorious over sin and death? Follow the signs, or drive off the road. The choice is entirely your own.