If it truly is a ranking system that appeals to whatever is a feel good system for encouraging people to participate would be good.
In the Pirates: Tides of Fortune game a player earns their way from half-drowned prisoner to legendary Scourge of the Seven Seas ! That is automatically generated from points earned from participation. ( Legend Fame Rankings )
However,
The leader of the Brotherhood and the advisors, can assign the members a designation in the BH based on several factors. Not just participation in the different areas of the site, but interaction with other members, behaviour, attitude, etc. .
The structure of the Brotherhood ( highest to lowest ) is : Leader, Brotherhood Adviser, Commodore, Swashbuckler, Ambassador, Coxswain, Scout, Boatswain, Boatswain's Mate, Crewman, and Cadet.
And there is an "Applicant" status too. A person applies to join and IF certain conditions are met , the Leader and the advisors can accept the applicants request and classify the applicant as a member --- starting off as a cadet.
These are flexible. You don't participate for a certain amount of time, or become un-ruly, you lose ( as an example ) Commodore status, and become something lower. Someone that hasn't participated ( or even merely haven't signed into their accounts for a given amount of time ) all become Cadets.
Advisor status is the highest that members can be given only by the Leader. Even then, it is a small, limited group who also are given specific privileges. Only two have full privileges / ability to do just about anything. The other advisors ( a small number of ), have limited moderating abilities , and solve personal issues the members might be experiencing .
Of course the whole system would have to be Time Travel related ; earn your way to become a Scourge of the Multiverse.