Message hats are magic items created by hat magic that can be used by anyone, including non-casters to send and recieve small items, like messages and gems. They are divided into two categories. Abjure hats are for sending and conjure hats are for receiving. Some hats are dual use, able to both send and receive. To send something, the user must wave the wand associated with the hat and say "Hoffa". To receive, the other person must wave their wand and say "Livingstone".
Real World References
"Hoffa" is a reference to a Teamster leader who famously disappeared. "Livingston" is a reference to an explorer who was famously found.