Sign of the dove?

The sign of the dove was instituted before the creation of the world, a witness for the Holy Ghost, and the devil cannot come in the sign of a dove.

The Holy Ghost cannot be transformed into a dove; but the sign of a dove was given to John to signify the truth of the deed, as the dove is an emblem or token of truth and innocence.

I had truly thought alot about that and am glad to have it clarified.