I think it is a thought into the relationship between death and love. By saying "I will follow you into the dark," the artist is trying to say that he is unsure of what will happen after death, and doesn't expect his love to be sure either. 'Dark' I think represents an unknown. So by saying "I will follow you into the dark," the artist is saying "I will follow you into the unknown," or even "into nothing," because he doesn't care if there is nothing as long as his love is there with him.
The part about "vacancy signs," I think is saying that he trusts in his beliefs, but if what he believes doesn't accept them together, he will face the resulting nothingness. He will go into a scary, dark, and ultimately unknown place for her, because there is nothing else that matters but her.
Overall, the song is trying to express the deep emotion that the artist feels toward his love, and how he would be willing to face anything for her.
I think it is a thought into the relationship between death and love. By saying "I will follow you into the dark," the artist is trying to say that he is unsure of what will happen after death, and doesn't expect his love to be sure either. 'Dark' I think represents an unknown. So by saying "I will follow you into the dark," the artist is saying "I will follow you into the unknown," or even "into nothing," because he doesn't care if there is nothing as long as his love is there with him.
The part about "vacancy signs," I think is saying that he trusts in his beliefs, but if what he believes doesn't accept them together, he will face the resulting nothingness. He will go into a scary, dark, and ultimately unknown place for her, because there is nothing else that matters but her.
Overall, the song is trying to express the deep emotion that the artist feels toward his love, and how he would be willing to face anything for her.