I work at a place where signature blocks - name, rank, duty position, three phone numbers, three email addresses - are mandatory. It really hacks me off when people who don't work with my organization don't use signature blocks when I have to work with them. How the heck am I going to get in touch with them other than via email?
Outside of that, it's nice if there is no user name, or it's official. I don't bother with signatures here, because there's no real reason for people to identify me beyond my user name.