Mat 12:39 But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas:
Mat 12:40 For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
Mat 12:41 The men of Nineveh shall rise in judgment with this generation, and shall condemn it: because they repented at the preaching of Jonas; and, behold, a greater than Jonas is here.
However, the Scriptures do also tell us that there will be 'signs following.' But to 'seek' a sign, is unbelief, for HE has come.
Mat 4:7 Jesus said unto him, It is written again, Thou shalt not tempt the Lord thy God.