In this forum you can tag a user: @user and a dropdown menu appears so you can select the username before entering the whole nickname.
In my forum I can tag users but no dropdown menu appears. What could be the issue?
You cannot do so, because it is no standard feature
But nearly all non-standard features are available as free plugins, too. See that one: http://vanillaforums.org/addon/mentionslookup-plugin
Thanks @R_J, it worked!!
You have to thank @x00