Make thee a fiery serpent. A saraph. The Septuagint, not understanding the meaning of saraph, has simply ὄφιν (cf. John 3:14). Set it upon a pole. גֵם Septuagint σήμειον. Vulgate, signum. The same word is better translated "ensign" in such passages as Isaiah 11:10; "banner" in such as Isaiah 60:4; "standard" in such as Jeremiah 51:27.
The "pole" may have been the tallest and most conspicuous of those military standards which were planted (probably on some elevation) as rallying points for the various camps; or it may have been one loftier still, made for the occasion.