Non-public boxes emptied by Royal Mail do not need to carry a cypher. Royal Mail write-up boxes produced since 1994 have the wording 'Royal Mail', Usually higher than the aperture (lamp boxes) or about the door (pillar boxes). In advance of this date all write-up boxes, except the Anonymous pillar https://cesarfdday.activablog.com/26439469/the-definitive-guide-to-letterboxes-melbourne