Vaera - Seeing Signs of Redemption

Why was it proper for Pharaoh to ask for a sign from Moshe when he asked to let the Jewish people go? Why did Noach, Chizkiyahu and Chananya, Mishael and Azarya receive signs? What is the concept of a 'sign?' What is the significance of Chizkiyahu and Chananya, Mishael and Azarya being saved specifically on the night of Pesach? What is the concept of this night that is 'saved' by Hashem for the righteous for salvation, and also for the future salvation of the entire Jewish people? How do we merit to see signs and merit to be called 'people of the sign?'