What two signs did God show Moses?
The first sign was throwing down the rod, which became a serpent, then picking it up as a rod again. The second was placing his hand in his bosom, where it became leprous, then removing and replacing it whole. Both were given to convince Moses that God meant what He said.
Les explains that in Exodus 4, Moses continues to debate the issue with the Lord, saying he is not eloquent, is slow of speech, and of a slow tongue. God answers by asking who made man's mouth, who makes the dumb, deaf, seeing, or blind, and then tells Moses to go, promising to be with his mouth and teach him what to say. Les points out that God had already used signs to convince Moses that he would be led of God: throwing the rod down so it became a serpent, picking it up so it became a rod again; and placing his hand in his bosom so it became leprous, taking it out and putting it back so it was whole. These signs proved to Moses that God indeed meant what He said.