Kautilya's Arthashastra 2.34.9

2.34.9

lubdhakaśvagaṇinaḥ parivrajeyur araṇyāni //

Hunters with their hounds shall reconnoitre forests. At the approach of thieves or enemies, they shall so hide themselves by ascending trees or mountains as to escape from the thieves, and blow conch-shells or beat drums. As to the movements of enemies or wild tribes, they may send information by flying the pigeons of royal household with passes (mudrá) or causing fire and smoke at successive distances.