In general some legal documents must be signed. So what determines whether a signature on such a document requiring to be signed is valid or not?
More specifically, is a signagure that is completely illegible invalid, or does a signer have more or less total latitude to define what their own signature looks like, however legible or indecipherably sloppy? If indecipherably sloppy signatures are acceptable, must there then be at least some clear indication somewhere on the document as to whose identity the signature is meant to convey, like a printed name above or below it?
This would seem to depend in turn on what the purpose of a signature is: authentication seems one very commonly intended purpose in which case it seemingly ought to be possible for a recipient or reader of the document to be able to compare the signature with signatures on other documents that are by the same person as is thought possibly to have signed the document in question.
Or is it to provide accountability so that the document can be certainly ascribed to a certain individual in case there are questions about the document to be addressed to its author/signer? For example, suppose a document is issued in the name of a company, and a director signs the document with their own personal name, but their customary signature happens to be utterly illegible, and the company in fact has multiple directors. In case the document becomes the subject of dispute in later legal proceedings, it seems that one would want to be able to cross examine the signer of the document as a witness in their personal capacity so as to ascertain the authenticity of the document and perhaps their true status as an authorised signatory for the company. In this case, it would be very helpful and indeed inportant to the recipient to be able to know whose signature that is on the document it is in fact intended to be.
So, what are the basic purposes of certain documents requiring signatures, and what makes a signature valid to fulfill these requirements?