Unfortunately "Graphology" is a pseudo-science and has no basis in fact.
You can tell a few obvious things, such as writing with the left hand, which was actively discouraged until the second half of the 20th century.
The other main thing you can normally work out is whether the person was accustomed to writing, though beware, because I know that a borrowed pen can make my signature look weird.

Remember that a person's writing will have a great similarity to that of the person who taught them.
AND remember that you won't see anyone's signature on any GRO certificate.