Actually, the attribution is not that simple. Roman whistles are historically very interesting objects that still hold many mysteries for us.
The use of whistles by the Romans is documented in many archaeological finds. Excavations at legionary encampments suggest a military use of the types of whistles found there. But the exact function is not clear and much disputed among archaeologists and collectors alike. Whistles might have been used to transmit commands on the battlefield or just for training purposes. It is also speculated that they were used for the hunt, for sports, music or rituals. Long story short, the use of whistles in Roman times is not fully understood.
Here is an example of a Roman military whistle:
(Roman military whistle, 1st to 2nd cent. AD)