1 Samuel 10:2-8

(2) When thou art departed from me today, then thou shalt find two men by Rachel's sepulchre in the border of Benjamin at Zelzah; and they will say unto thee, The asses which thou wentest to seek are found: and, lo, thy father hath left the care of the asses, and sorroweth for you, saying, What shall I do for my son? (3) Then shalt thou go on forward from thence, and thou shalt come to the plain of Tabor, and there shall meet thee three men going up to God to Bethel, one carrying three kids, and another carrying three loaves of bread, and another carrying a bottle of wine: (4) And they will salute thee, and give thee two loaves of bread; which thou shalt receive of their hands. (5) After that thou shalt come to the hill of God, where is the garrison of the Philistines: and it shall come to pass, when thou art come thither to the city, that thou shalt meet a company of prophets coming down from the high place with a psaltery, and a tabret, and a pipe, and a harp, before them; and they shall prophesy: (6) And the Spirit of the LORD will come upon thee, and thou shalt prophesy with them, and shalt be turned into another man. (7) And let it be, when these signs are come unto thee, that thou do as occasion serve thee; for God is with thee. (8) And thou shalt go down before me to Gilgal; and, behold, I will come down unto thee, to offer burnt offerings, and to sacrifice sacrifices of peace offerings: seven days shalt thou tarry, till I come to thee, and shew thee what thou shalt do.

All these signs were intended to convince Saul, that in all Samuel did, he had acted under the authority of God. And no doubt they had their effect by way of confirmation.