The 'mention' tags, or @ tags, will not become active unless the tagged username is typed identically to its state within our member base list. This means that care must betaken to include any spaces where they exist in a username, and no other character that is not present in a username may be added to the tag (or it will be rendered inactive). For example, a period "." can not be appended to the end of an @ tag if it is not actually part of the username. Even if the tag is placed at the end of a sentence, leave any nonexistent punctuation off. As a specific example, if I type @Mr Peepers the tag should activate fine. Whereas if I type @Mr. Peepers it will not. I'm confident that we will all get used to the tagging system here together
EDIT: There is also a chance that an @ tag may not activate with a certain font color, size, and style enabled. This seems to be one of the drawbacks in allowing our members to select their own font formatting here