When did national callsign designations with prefix letters begin? For example, 2ANU (~1909) became W2ANU, for the club station at Erasmus Hall High School in Brooklyn, NY. 2CLE (~1909) became W2CLE, for the club station at Stuyvesant High School in NYC. When did the practice of issuing new callsigns with W begin? Thanks. 73, Lew N2RQ at arrl.net