So the following document is either not correct, or there's a bug in the Moodle 2.6 forums.
https://docs.moodle.org/26/en/Additional_name_fields
I want all surnames in moodle 2.6 to be displayed before the firstname. However, the Moodle 2.6 forum will refuse to listen for STARTED BY to fullnamedisplay var as set in the User Policies. It keeps the firstname first, and the surname last like default.
The workaround is to go into the language pack search for fullnamedisplay in the String Identifier field, and then swap {$a->firstname} {$a->lastname} to {$a->lastname} {$a->firstname}.
My guess is that the forum module doesn't listen to fullnamedisplay for this particular string.
Anyway, I'm probably the only one that wants lastname's to be displayed first..
Hope this helps someone