'Sign' in the Bible

"'This shall be the sign to you: You shall eat this year that which grows of itself, and in the second year that which springs of the same; and in the third year sow, and reap, and plant vineyards, and eat its fruit.

Hezekiah said to Isaiah, "What shall be the sign that Yahweh will heal me, and that I shall go up to the house of Yahweh the third day?"

Isaiah said, "This shall be the sign to you from Yahweh, that Yahweh will do the thing that he has spoken: shall the shadow go forward ten steps, or go back ten steps?"