 As railroads became more developed , Billboard set up a mail forwarding system for traveling entertainers . The location of an entertainer was tracked in the paper 's Routes Ahead column , then Billboard would receive mail on the star 's behalf and publish a notice in its " Letter @-@ Box " column that it has mail for them . This service was first introduced in 1904 . It became one of Billboard 's largest sources of profit and celebrity connections . By 1914 , there were 42 @,@ 000 people using the service . It was also used as the official address of traveling entertainers for draft letters during World War I. In the 1960s , when it was discontinued , Billboard was still processing 1 @,@ 500 letters per week . 
