Then you have to worry about falcons, or Blackadder. Smoke signs, maybe... but then you have to worry about the weather and wild fires... Seems they thought that one through!
What about flag signaling? Asking for a friend.
Ok as long as you don't use a halyard, since rope could be considered wire.
Pigeons would probably fall under `mail fraud`.
If the laws of USPS made during 1800s pigeon mail carrier are still on the book, then yeah, mail fraud.