In the very early days of ham radio the distances over which signals could be detected was small. There were also very few "amateur experimenters' on the air and so the need for identifying a particular station was small. Then, as distances increased and more people started to use the new wireless or Hertzian waves, the need arose for stations to identify themselves in a unique way. Initially they invented their own callsigns, but later the authorities stepped in and started to issue them in a more coordinated fashion. Find out the story of amateur radio callsigns: https://www.electronics-notes.com/articles/history/amateur-ham-radio/first-callsigns-introduced.php
