I love the chapter in Robert Silverburg's Dying Inside is where the main character, Selig, who actually is psychic has a class at school where ESP is discussed. The teacher has the whole class try to read her mind as she looks at a set of Zener Cards. Of course she is just using the exercise to teach the class about statistics (4 out of 20 would be average) but poor Selig is so paranoid about anyone finding out his true abilities he purposefully gets every card wrong! Hes is almost rumbled as the chances of getting all 20 cards wrong was even lower than getting 6 or 7 cards right. Standard Zener Card Set

So why am I talking about random science fiction again? Well the reason Zener Cards are used by "psychics" each shape is very distinctive from the others and this is the aspect which we'll put to use in the Pigeon Post system.

Pigeons should fly at a minimum height to avoid structures and trees until they reach the target destination. This could be a little out as GPS has a 10m margin of error so the Pigeon will hover over a destination point and "look" down. As each element of the physical system has a reflective or glowing Zener shape on the top surface the Pigeon should recognise what it is hovering above as it lowers down. When it gets within a couple of metres it will be close enough to ping the RFID tag. If it is unable to connect with the RFID it can lower further, grip the connector and read the QR code printed on the top of the Case or Coop.

The triangular shapes can be placed pointing towards each element to help the Pigeon zero in and rotate to the correct angle to grip the connector.