It is likely that Joseph Smith (and most Christians) would associate the symbol of a serpent with the Devil, as per the story of Adam and Eve in Genesis. However the symbol of a serpent was a dual symbol in the ancient world which could represent the Devil or Deity.
In the Book of Mormon, the symbol of the serpent is used both positively and negatively. Positively in 2 Nephi 25:20
And now, my brethren, I have spoken plainly that ye cannot err. And as the Lord God liveth that brought Israel up out of the land of Egypt, and gave unto Moses power that he should heal the nations after they had been bitten by the poisonous serpents, if they would cast their eyes unto the serpent which he did raise up before them, and also gave him power that he should smite the rock and the water should come forth; yea, behold I say unto you, that as these things are true, and as the Lord God liveth, there is none other name given under heaven save it be this Jesus Christ, of which I have spoken, whereby man can be saved.
And spoken negatively in 2 Nephi 2:17-18
And I, Lehi, according to the things which I have read, must needs suppose that an angel of God, according to that which is written had fallen from heaven; wherefore, he became a devil, having sought that which was evil before God. And because he had fallen from heaven, and had become miserable forever, he sought also the misery of all mankind. Wherefore, he said unto Eve, yea, even that old serpent, who is the devil, who is the father of all lies, wherefore he said: Partake of the forbidden fruit, and ye shall not die, but ye shall be as God, knowing good and evil.
How did Joseph Smith know about this dual symbolism?