You can leave the group from the same page you joined the group.
Unfortunately, in order to exclude SZ from searches completely, I must hide the forum completely. The permissions don't seem to work as advertised. :(
I think I can make it clear that the forum exists, but can't be read by those who don't join the group. I'll be updating descriptions to show how to gain access to the group.
Not going that route - no time to fiddle with a bunch of individual access masks.
IF it becomes a problem, we can...
And to my normal (test) user, I see the name ANonymous, the user id Anonymous, and the avatar of the eyes in a dark room with a ? over them.
It works. ;)