In emails and on the internet, sometimes people write signature with full first name and last initial, sometimes first initial and full last name. Is there any difference between the two or is it purely personal preference?
E.g. for the name John Smith, when would one use John S and J Smith, respectively?
In my experience "J Smith" is used more often than "John S". For example, when quoting someone it's common to just use initials for all their names, except the surname. e.g. "C. S. Lewis".
I haven't come across "John S" very often. I guess someone might use it for confidentiality reasons... e.g. reception staff at my work do that on their name badges.
Generally calling someone by their first name is more friendly/informal, whereas calling them by their surname is more formal. What you use in your own signature is personal preference but it's worth knowing this general convention so that you come across how you are intending (e.g. in a job application I'd use both my first name & last name, whereas in a email to a colleague, just my first name).
Email signatures are very freeform when they don't follow perfect letter standards. It tells you a little about how they think of their name relative to you. In many cases, it's a pretty strong guess as to how you should call them.
The last initial is more rare than the first or middle initials, and it usually has to do with either anonymity or space. For example, in an office of two Johns, John Smith and John Psmith, their belongings might be labeled John S and John P, to save space and trouble.
