'Sign' in the Bible

The Pharisees came out and began to question him, seeking from him a sign from heaven, and testing him.

He sighed deeply in his spirit, and said, "Why does this generation seek a sign? Most certainly I tell you, no sign will be given to this generation."

"Tell us, when will these things be? What is the sign that these things are all about to be fulfilled?"

Now he who betrayed him had given them a sign, saying, "Whoever I will kiss, that is he. Seize him, and lead him away safely."