3 Nephi 2:7

and nine years had passed away, from the time which the sign was given, which was spoken of by the prophets, that Christ should come into the world.

Nine years had passed since the sign was given. The prophets had spoken about this sign. It showed that Christ would come into the world.

Nine years had passed since the sign the prophets had spoken of—the sign that marked Christ’s coming into the world.