"If God gives me some ‘sign,’ then I will believe."
The unsaved often want a "sign" from God. This is in spite of the testimony of creation, their conscience, the Bible, and the Christian. The cross is the only thing that can truly convince a sinner of the reality of who Jesus is. Once they understand that the holes in His hands and His feet are there because of their own sin, they will fall at His feet and cry, "My Lord and my God!"