Why does it matter what letters appear in a signature?

I have one of those first names that has a common nickname associated with it. I’ve never gone by my actual given name, so I sign the name I commonly use. My signature is kind of a messier, stylized version of my normal handwriting, but you can clearly see that I’m not writing my formal given name.

That has created problems for me when I’m signing legal documents, like mortgage papers, because it really doesn’t come naturally to me to sign another name, and I sometimes screw up, much to the dismay of the signature wonks.

But then there are plenty of people whose signature bears no resemblance whatsoever to any known alphabetical scheme. No one looks at those signatures and says, “God save us, you signed ‘Bill” instead of ‘William’!”.

So why make a fuss about it?