'Sign' in the Bible

Then the Pharisees came and began to argue with Jesus, asking for a sign from heaven to test him.

Sighing deeply in his spirit he said, "Why does this generation look for a sign? I tell you the truth, no sign will be given to this generation."

"Tell us, when will these things happen? And what will be the sign that all these things are about to take place?"

(Now the betrayer had given them a sign, saying, "The one I kiss is the man. Arrest him and lead him away under guard.")