Initially amateur radio stations did not use callsigns. There was no need as so few stations were transmitting that identification in that way was not needed.
As the number of stations started to rise, so a more formal way of identification became necessary. Even though the distances being covered were still relatively small, the use of a callsign was a more specific form of identification than using a name - a little like using a handle on CB these days.
Before there was any mandatory use of callsigns, their concept started to be introduced.
With stations needing to make contact via Morse in the early days, giving a full name was rather long winded and first names could be duplicated.
The use of a callsign gave a nearly unique way of quickly identifying a station. Typically about three letters were used, often the operator’s initials.
First UK amateur radio callsigns
In the UK the Postmaster General, who was responsible for all wireless telegraphy reported on the increasing number of licenses grated for private experimentation with wireless systems to the British Parliament. There was a steady number of applications being submitted, most of which appear to have had licenses granted.
With the requirement for regulation of the first amateur radio licenses, or as they were known experimenters licenses, it was necessary to easily identify each station uniquely.
In the UK in May 1910, the Postmaster General sent out a letter to each of the holders of these first amateur radio licenses or experimental licences holders to inform them that he had: “ . found it desirable to lay down a general rule that each stations should have a distinctive call-signal and that each station, when signalling, should begin each transmission with the callsign of the station with which it desires to communicate and end it with its own callsign.”
Along with this announcement the ‘call-signals’ for each station - one for each location if one licensee had stations at more than one location - were allocated. These British first callsigns consisted of three letters.
First amateur radio callsigns in USA
The situation was rather different within the USA. There was no licensing of amateur radio stations within the USA until the Radio Act of 1912 became law.Until this time the early radio amateurs had allocated themselves callsigns on an adhoc fashion.
Despite this, the Modern Electrics magazine published a listing of US stations and their callsigns (self-assigned) in a 1909 issue of their magazine. It listed the name and broad location of the station along with the call-letter which normally consisted of three letters, although a number had fewer letters, one having just the letter ‘H’ and others having a number as well like ‘3B’. It also listed the approximate wavelength on which they transmitted along with the spark coil length or the transmitter power.
However as licenses became necessary the stations were issued with callsigns.
These were initially issued by the US Department of Commerce, and the Government Printing Office, published annual lists of all US radio stations - amateur, commercial, and government stations all being listed together.
Later, the US Commerce Department began issuing separate call books for amateur stations.