Indeed. The message tag box is the way to go.
When accessing the message board initially, I was not logged on and was not presented the message tags option.
Oddly enough, I was allowed to read messages and post/respond to messages without being logged on. However, while the post/reply window came up without being authenticated, I had to log on to actually save the post.
Once I logged on, the option appeared. Adding a hashtag in the message body does not do it.