Possible Clues:

• Part of address
• Indication of area in address
• Depots, for sorting, must have county included as part of address
• If it's indecipherable, won't your letters be delivered?
• Attachment of characters to very specific part of town?
• Part of address to aid sorting
• So haddock the chippie's future then? English homes all have one
• Letter sorting device (or kind of modern lottery?)
• Picket protocol for Dublin fifteen
• Letters and digits to aid sorting mail