Use of whistles to relay commands in battle

[M. Caecilius]

Just because they found a whistle does not mean it was purely a battlefield piece. Perhaps whistles were used by soldiers on 'police duty' within a city ~ just like our 'modern' concept of police.

Although at the moment I do not recall any surviving written evidence for whistles being used specifically by soldiers in such a role..?

The concept existed after a fashion: there is evidence for the 'police' forces using bells: "For those who guard communities at night carry a bell, in order to be able to signal to the inhabitants whenever they need to do so." (Cassius Dio 54.4.4). A single reference cannot, unfortunately, confirm or deny whether at some other time and place, or even conjointly, whistles were used. They do have the advantage that they don't take up a hand.

Max C.