I had no idea what the introductory posts were until I was on here for a few weeks and read someone else's post saying, "Do an introduce yourself post!" Since posting my own, I noticed that people often post a picture of themselves holding a sign with the date and Steemit on it. Obviously creating fake posts or abusing the introduce yourself tag is wrong, but I would also bet that a lot of new users just don't know how to do it the right way.