Miracles demonstrate the supernatural power of God over nature and evil forces. The word wonders refers to the response the miracles evoked in the observers, a response of astonishment and fear. Observers knew they had seen something out of the ordinary, something that in its greatness could even be threatening to them. There, Peter referred to the signs of Jesus. This word stresses that aspect of miracles which draws attention to the significance of the event.
Signs point to or reveal something else.
First, signs indicate a relationship between the miracle worker and God. Second, signs point to a fuller activity of God still to come. Also, miracles are revelatory themselves in that they expose the nature of God. Jesus came to reveal the Father to us. When just about anything is called a miracle simply because it's amazing, real miracles lose their significance.