According to the PHP code, it should trigger on announcement.php where the forumid is greater than -1. I.E. if the announcement is within a specific forum. If it isn't triggering then there is a bug somewhere. However, since vBulletin 3.X is end of life and no longer in development, the bug will never be resolved.
Got my answer from the big man This seems to be useless code, that was either missed for removal, or never implemented. (as far as we can tell)