A good way to know if your team is using their taskboard to really manage their work is to look at their daily standup meeting.
Does it look like this:
or like this?
A team that is using visual management to manage their work will always do their daily standup against the board. During the daily standup you update your team members on your work. Both work finished the day before and work still in progress should be clearly indicated on the board. It only makes sense to go over the board as you talk. This is both easier for you and easier for team members. It also helps to visually place what you are talking about in context.
If you are using the DONE tag, nametags, status tags and the three columns; then there is a very simple guideline to make sure you don’t forget to talk about anything important every day: do the daily standup against the board, and make sure all tasks in the middle column (“in progress”) are talked about.