The crowds are looking for another sign, and they get one here. John states this directly in John 6:14: "When the people saw the sign that he had done, they began to say, This is indeed the prophet who is to come into the world."
Jesus multiplies loaves of bread and fish to satisfy the hunger of the people and it is called a sign. (This is the third sign according to John's chronology with first being found in John 2:1-12-Turning water into wine and secondly in John 4:46-54-Healing of a royal official’s son.) In John's account of the Gospel of Christ, a sign is used to signify who Jesus is. In this miraculous feeding, the people see the sign and it signifies to them that Jesus is "the prophet who is to come into the world" (verse 14).
An interesting comparison to this should be noted in the words of the woman at the well (John 4:7-26). When confronted with the greatness of Jesus, she also calls him a prophet (John 4:19). Encountering Jesus. Expecting something. Receiving food to fill their stomachs. They are interpreting the encounter in terms of who Jesus is -- prophet -- but they want more. They want to make him king.
How often is it that people "come after" Jesus because of the signs? People observe the good that comes to those who follow Jesus. Expectations are awakened. We want the big things. Healing from horrible diseases. Instant money when the house is in foreclosure. A miracle for the child who cannot overcome addictions. Sometimes this is the miracle that we get.
How often is it, though, that all someone needs is a simple reassurance that, indeed, Jesus the Christ is present. That presence can get the boat to shore, can calm the grandest of fears.