This is the classic "rock-star" song about the performer who's made it big and is re-assessing his values and wondering if this is what he wanted in the first place. It opens with him negotiating terms of engagement with a groupie, who as the song notes is "too wild to care" with "animal stare", as if this is nothing new to her either and the singer is just another big-name scalp for her bedpost. He perceives the essentially shallow and meaningless nature of the encounter and realizes both of them are, indeed, just "goin' through the motions" of everything and playing their respective parts.
Yet he still has the meaningless sexual encounter anyway, shore of anything that would make it meaningful or worthwhile: just another day at the office, so to speak.
In the morning he writes her an autograph - knowing this is also playing the part and doing what's expected of him - and a little humanity reasserts itself as she weeps and asks to stay.
But he realizes the autograph is just going to go into a book and she might take it out and look at it in twenty years' time and try to remember a name and a face. And this reminds the rock star of his own mortality and the fact his place in the world isn't all that exalted, when he comes to look at it.