First Ham Radio Callsign History Website:

Initially amateur radio stations did not use callsigns, but as the numbers of stations increased along with regulation and licences, so callsigns were introduced. 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.

from Ham Radio Times http://ift.tt/2tLip7i
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