This is an example of where the person who came up with a term screwed up. You're talking about how you sign your email, but the post is talking about the signature line (or lines), which are not a substitute for signing your message.
For personal emails I don't use a signature, I just sign it. For business emails I sign the email and have a signature line with my name, title, business group, phone numbers, and group website. --This information fits on one line and is easy to refer to or ignore as per the recipient's needs.
Four lines is not short. Nobody cares about your blog, Twitter, or LinkedIn.
I sign my emails either "--Jon" or "Regards, Jonathan Rockway" depending on who the intended recipient is. If you want to read my blog, just type my name into the nearest search engine.