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call sign
mil., logist.	Any combination of characters or pronounceable words, which identifies one or more communication facility, a command, an authority, an organization, or a unit; used primarily for establishing and maintaining communications. (FRA)
USA	Any combination of characters or pronounceable words, which identifies a communication facility, a command, an authority, an activity, or a unit; used primarily for establishing and maintaining communications (JP 3-50)

call: 4 phrases in 1 subject

Abbreviation

4