Experience tells me that newbies hardly read the FAQ.
As such it'll be more work for the mods and admins to fix any problems caused by signatures.
Besides, the main emphasis of this place is content, not fancy display of the content. Early on, even avatars were out of the question.
Also, Seph3D's method of including a signature is out of the question.
If every member did that, the search function would lead to lots of false results.