'Sign' in the Bible

And this shall be the sign unto thee: Ye shall eat this year that which groweth of itself, and in the second year that which springeth of the same; and in the third year sow ye, and reap, and plant vineyards, and eat the fruit thereof.

And Hezekiah said unto Isaiah, What shall be the sign that Jehovah will heal me, and that I shall go up unto the house of Jehovah the third day?

And Isaiah said, This shall be the sign unto thee from Jehovah, that Jehovah will do the thing that he hath spoken: shall the shadow go forward ten steps, or go back ten steps?