Let’s use, as a working definition of Their Signature; “somebody's name written by him or her in a characteristic way”. Long ago, about a decade, I was often asked to provide “legible” signatures that matched the name signing. I tried that a few times, mostly with dismal failure. More often than not, the signature was totally illegible – more like artwork than written script handwriting.
Now let’s go back a lot further in the past, about two thousand years. Commercial transactions were common then as they are now. Most did not read or write, they made their mark. It was the seal of the Notary, who knew the affiant that validated the “mark”. Nothing has really changed. It is still the Notary who is supporting the validity of the signature.
They can sign many ways, with a pen, with a brush (artsy?), using their hands, feet, knees or mouth to hold the instrument of signing. Keep in mind the Americans with Disabilities Act. We must make reasonable accommodation to all who qualify for our seal. The signature does not have to be the same as, or even similar to the one on their ie: driver license. A lost limb or even both arms does not preclude notarization. Pen held in mouth is fine, the signature will be vastly different – but that really does not matter. Many elderly people have hands that shake, but their minds remain crystal clear.
Their “signature”, however written is the second aspect of accepting the Notary Oath. The first part is communicating a “yes” to the Oath; the signature is the written agreement. As mentioned – often the signature does not match the ID. Of course the picture must. There is one signature that (at least in NY State) must match – and that one is mine. My signature is recorded with the county clerk and for it to be authenticated; my signature on the document must be the same as my officially recorded one. Thus my signature cannot change.
To me what really counts is their printed name somewhere to indicate exactly who is being notarized. If it’s in my “loose ack” – I get to print the name. Sometimes it’s not that clear on the document, that is when I ask them to print their name under their signature. Notaries must take care to delimit their notarization to those actually given the oath and ID checked. When there are “other” places for signature, I often add “by affiant name” to the “sworn to and subscribed”.
Signatures vary greatly. I have seen perfectly formed cursive handwriting, squiggles and minor works of art with flourishes. Many bear no relation whatsoever to the name. Sometimes the same thing is on the ID, sometimes not. It’s my job to determine who they are, not to critique how they write their name. It would be so much more “absolute” if a DNA sample were to be added. Some think a thumbprint would be best; but not everyone has a thumb.
So, I am not a handwriting nanny. When the instructions mandate “clearly written” I tell the affiant what they “require” – and accept what they do. Usually I ask for their routine, standard signature “the way you would sign a check”. In my experience people object to being told “how to sign”. The signature, stamp and seal of the Notary makes whatever it is “Kosher”.