Well, some of the birthsigns such as the Atronach had some pretty major impact on how you played and added a nice touch of customizability. I sure hope they're still in-game like a starting perk, it wouldn't really feel plausible to "choose" what sign you were born under at any later point.

If by that you mean the answer can only be found deep within the foul intestines of Hermaeus Mora, then yes.