Seven signs in the Gospel of John
Structure of John
There is a widespread scholarly view that John's gospel can be broken into four parts: an introductory part (John 1:-1:18), the Book of signs (1:19 to 12:50), the Book of exaltation (13:1 to 20:31) and an epilogue (chapter 21).
John 20:30 Therefore many other signs Jesus also performed in the presence of the disciples, which are not written in this book; 31 but these have been written so that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name.
It is this indication by the author of the Gospel that the signs are selected which leads to the examination of them as a sequence and the numbering "seven".
The 7 signs
The seven signs are:
- Changing water into wine in John 2:1-11
- Healing the royal official's son in Capernaum in John 4:46-54
- Healing the paralytic at Bethesda in John 5:1-18
- Feeding the 5000 in John 6:5-14
- Jesus' walk on water in John 6:16-24
- Healing the man born blind in John 9:1-7
- Raising of Lazarus in John 11:1-45
The seven signs are seen by some scholars and theologians as evidence of new creation theology in the Gospel of John, the resurrection of Jesus being the implied eighth sign, indicating a week of creation and then a new creation beginning with the resurrection. 
The crucifixion as the 7th sign
Others, such as John Marsh and Stephen Smalley, have credibly suggested six initial signs (the walking on the water not a sign in itself), and the seventh sign as the crucifixion. 
The 8th sign
- The Cradle, the Cross, and the Crown: An Introduction to the New Testament by Andreas J. Köstenberger, L. Scott Kellum 2009 ISBN 978-0-8054-4365-3 page 305
- The Bible Knowledge Commentary by John F. Walvoord and Roy B. Zuck 1983 ISBN 0-88207-812-7 page 269 
- Rob Bell, Beginning in the Beginning, Poets Prophets & Preachers 
- John Marsh, Saint John (Pelican New Testament Commentary, 1968) p.65, Stephen Smalley in The Oxford Companion to the Bible, (OUP, 1993) p.373
- John Hutchison, Our Lord's Signs in St. John's Gospel: Discussions Chiefly Exegetical and Doctrinal on the Eight Miracles in the Fourth Gospel (printed Edinburgh, 1892)
- Bullinger Companion Bible Eight Signs in the Gospel of John