There is also a setting that will display a configurable line of text. Html has been added so you can put a link in it.
Ie message might be
To post you must be a member. Request to Join?-(link)
This is one from mine
To participate in category you need to <a href="/g/Pimaxians/members">Apply</a>
The link could also be a Topic that explains how/if access can be achieved