Tagging someone

[Steve Ashton]

Tags and tagging as defined by the vBulletin software that X Marks uses is defined as -

"A tag is a metadata keyword or term string attached to a content item. Once the tag is attached, it can be used in a search for content.

vBulletin tagging allows users to apply their own keywords (tags) to most content types. This allows users to categorize items based on their actual content.

Tags can contain any character except a comma, which is used to separate multiple tags. Additionally, you cannot add tags with the following characteristics.

• Have less than an administrator-specified number of characters. The default is 3.
• Have over 25 characters. (This is the default value. You can change it with the "Tag Maximum Length" option.)
• Contain any censored words.
• Are in a list of common words that you create yourself."

This is significantly different that other forms of tagging on other social media such as Facebook.
Tags within vBulletin are a way to help in searching for a topic, while tagging in Facebook is a way of tracking activity.

Here is how Facebook defines tagging -

"A tag is a special kind of link. When you tag someone, you create a link to their timeline. The post you tag the person in may also be added to that person’s timeline. For example, you can tag a photo to show who’s in the photo or post a status update and say who you’re with. If you tag a friend in your status update, anyone who sees that update can click on your friend’s name and go to their timeline. Your status update may also show up on that friend’s timeline. When you tag someone, they'll be notified. Also, if you or a friend tags someone in your post and the post is set to Friends or more, the post could be visible to the audience you selected plus friends of the tagged person. Learn more. Tags in photos and posts from people you aren't friends with may appear in timeline review where you can decide if you want to allow them on your timeline. You can also choose to review tags by anyone, including your friends. "

I believe that the OP is asking about the second type of Tagging. The type that is for tracking the activity of a person.
This is not how tags work on vBulletin which is an aid in doing a search on a topic you are interested in.