In Exd 17:15, Moses, recognizing that the Lord was Israel's banner under which they defeated the Amalekites, builds an altar named Jehovah-Nissi (the Lord our Banner). Nes is sometimes translated as a pole with an insignia attached. In battle opposing nations would fly their own flag on a pole at each of their respective front lines. This was to give their soldiers a feeling of hope and a focal point. This is what God is to us: a banner of encouragement to give us hope and a focal point.
Blue Letter Bible