As I read this chapter, I was struck by how appropriate the signs of the coming and death of Christ were. I love that the birth of Christ is represented by light. Days without darkness seem to be an appropriate symbol for the glorious coming of the savior. He represents the light and life of the world. And so of course it is appropriate for his birth to be marked by light.
And the symbol of his death is likewise striking. It also might have had special resonance for the Nephites because of its symbolic link to the plague of darkness which was one of the 10 plagues against Egypt. This darkness might have also reminded those listening to Samuel of the recent conversion of the Lamanites amidst a cloud of darkness.