This is the 5519th most frequent Russian word.
позывным
"Позывным" means "call sign" in English.
In this sentence, 'позывным' refers to the call sign used to identify an individual during a specific scenario.
Его позывным во время операции был «Орёл».
His call sign during the operation was 'Eagle'.
Here 'позывным' indicates the identifier broadcasted for communication purposes.
Мы слышали позывным его сигналы по радио.
We heard his signals through the call sign on the radio.
In this usage, 'позывным' denotes the symbolic identifier selected to represent someone's persona or role.