They’ve brought it up repeatedly. Wes, Angel, Spike and a few others have wondered if the Shanshu prophecy is actually about Spike.
When he first learned of the prophecy, Spike asked what it said. Then ‘It doesn’t say Angel? It just says vampire with a soul?’
In the episode (I can never remember the titles) in which Angel is having nightmares due to a demonic leech, he dreams that he has failed and is forgotten while Spike fulfills the prophecy and becomes human again.
In another Spike and Angel are led to believe that the vampire with a soul will become human again after drinking from a magical chalice. They rush to the chalice and fight for it. Spike argues the prophecy is really about him. The chalice turns out to be a fraud.
They’ve broughtn up the fact that the prophecy could be about Spike about as often as they bring up the fact that Angel broods.