Now that you mention it @hark that is called a mention. I have no idea what tagging is other than tagging photos on Flickr so people can find it if they are looking for a certain image.
ie.. If you put up a picture of lets say a tiger, then you can tag it as #animals #zoo #tiger.
Hmmm, thought I had an activity accomplishment in the past month for tagging, and just assumed it had to be the mentions because...what else do I do here?
Whenever you start a thread there is a place to add tags, up to five of them. This helps others when they search for things. Each tag word helps members find info related to their search.
So your tagging class is based on your putting tags with every new thread your start, or even when you post tags for an existing thread that lacks tags. Like I said it's all designed to help others in their searches.
When you start a thread, the system picks up the title words and makes them tags. You can see them at the bottom of a thread window. Anyone can add more tags, but the auto tag is working in the background.
I have never added a tag to any thread, but all my threads have tags, so it's either the system, or someone running around behind me. However, I am a Tagger Second Class, so maybe I am a sleep tagger.