Let's say I have the following arrangement:
1. Liquid Investments
'Investments' is a group, and 'Liquid Investments' is a forum, containing 'stocks', 'bonds', and 'commotities' as sub forums.
I am concerned that this arrangement might confuse some people, resulting in a topic being placed in the wrong forum.
What I would like to have instead is 'Liquid Investments' as a sub group, where you cannot post directly to it. If I want a forum for miscellaneous Liquid Investments, I would simply add that as an additional forum within the 'Liquid Investments' group.
I can get the functionality I want by locking the 'Liquid Investments' forum, but I'd rather not do that because the lock symbol might cause some confusion.
Is there any other way to achieve the result I'm looking for?
As you already have figured out, there's no such thing as sub-groups. If you do lock the "Liquid Investments" forum you should be able to select a different image or icon for the forum when its locked - one that doesn't have a "lock" on the image. But that still doesn't mean that users wouldn't sometimes try to post in it. You could add one post to the forum that gives them links to the other forums so if they do try to post in it, there's at least some info as to why they can't do that.