But the current locked entry is a padlock (lock, on the list), so having it just be a key doesn't seem to fit - the key's the opposite of the padlock, isn't it? And IIRC if you're seeing someone else's locked posts, you see the padlock whether it's on a filter or not, so this would only be for confusion for the journal owner.

group_key, maybe - I like table_key, for "this is the list of people with the key". A table and a padlock would be even better, but that's not on the list (probably too hard to get a recognizable lock that small).