The variable mob_clan under CHAR_DATA seems to not be set anywhere except in guard recruitment. However, it's called in a few places to check mob resources being killed by same-clanned PC's and to restrict customs from pulling weapons from same-clanned PC's.
I've devised the following improvisation to set the mob's clan on resetting the area. This provides for an automatic method instead of necessitating the need to set each individual mob. This was added to reset_area, but I'm using the old reset code, so I'm unsure where this would apply at under the new reset system.
char_to_room( mob, pRoomIndex );
if( mob->in_room && pRoomIndex->area->planet && pRoomIndex->area->planet->governed_by )
STRFREE( mob->mob_clan );
mob->mob_clan = STRALLOC( pRoomIndex->area->planet->governed_by->name );
economize_mobgold( mob );
level = URANGE( 0, mob->top_level - 2, LEVEL_AVATAR );
if( mob->vip_flags != 0 && pArea->planet )