One of the early followers of Jesus wrote these words about signs, “Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.”-John 20:30-31
When the writer of John uses the term “sign” he is talking about particular signs that we might describe as miracles: Turning water into wine; feeding 5000; healing a blind man; raising a dead man. But these signs all point to one thing, that Jesus is the messiah. These miracles also contain a hope, that upon following them belief in Jesus will occur and that new life will be received.