Okay, but Night Mother, and other figure heads are known throughout the whole franchise, and I'm sorry if you found that spoilerish, but then again you have to be careful for what you will read, and I made sure not to make it the first thing in my post, but the last, so if you don't want to know anything about the Dark Brotherhood, you shouldn't of finished reading my post.
Also I was paraphrasing what the guard said, he didn't actually call me the Night Mother.
If there really is something spoilerish, like if a character is going to die or if there is a quest that I'm asking about I will always make sure to spoiler mark it, but a common figure head of a faction, everyone knows about is hardly a spoiler. That's like saying, There are Oblivion gates in the game Oblivion. It was always known, even though you will discover about it in the game later on.
But I digress, then I might as well tell you not to look at the forums, because if you think Night Mother is a spoiler, then you shouldn't be here.