David"s actual complaint appears in Psalm 86:14. Rebels against God and His anointed king were harassing David. He contrasted their characters with God"s. Specifically, David needed strength of all kinds to deal with these opponents. The sign he requested would have been some physical, tangible proof that God was supporting His servant. God"s deliverance would constitute such a sign. [source][source][source]
This is a prayer for help from a very mature believer. David"s understanding of God resulted in his taking a humble place of submission to His Lord. His confidence during his trial was strong because he knew how great and loyal God is. Rather than exhibiting panic in the face of danger, David demonstrated peace, confidence, and even joy. [source][source][source]