From Longman Dictionary of Contemporary Englishcall signˈcall sign noun [countable usually singular] (also call letters especially American English) TCa name made up of letters and numbers, used by people operating communication radios to prove who they are
Examples from the Corpus
call sign• Her call sign was Gaslight Lil and his was Popeye.• I was developing the habit of calling everything by its call sign.• And you know Omega's call sign, don't you?• The number six in the call sign always meant boss, chief shit.• He tapped out the call sign in two-minute segments, waited for ten, called again. 