NF Jon of
waindigo (XF username) did this for me. It's a template edit.
The moderator appears as avatar + username below with link to profile
+ the word MODERATOR above the avatar pic.
This is located with the title of the page.
You can see my top title area here
http://www.housemorgain.co.uk/circle/forums/reviews/
but it is not standard XF.