This short explanation of callsigns is primarily for non-amateur radio operators.
A callsign is an alpha-numeric code, such as N2XJ or KC2IBB, which is assigned to each licensed amateur radio operator (ham) by the appropriate radio licensing agency of the operator's government. (In the United States, the Federal Communications Commission, or FCC, makes callsign assignments.) Every ham is assigned a unique code, so that -- throughout the world -- no two hams have the same code.
Callsigns are usually 4 to 6 characters long with at least one number in the middle of the characters. The first 1 or 2 characters -- the prefix -- indicate the ham's country. Each country has been assigned a series of unique county prefixes. For example, in the United States, hams callsigns begin with one of three one-letter prefixes -- K, N or W -- or a two letter prefix in the ranges AA-AL, KA-KZ, NA-NZ, WA-WZ. In Canada, callsigns usually begin with VA-VG, VO or VX-VY, while in Mexico they begin with XA-XI.
The number in a callsign usually indicates a region in the country. For example, 2 is assigned to US hams who are living in NY or NJ when their license is issued.
The last 1 to 3 callsign letters -- the suffix-- normally have no particular meaning and are sequentially assigned to new licensees. (In 1996, the FCC began the "vanity" call sign program, which allows hams to apply for any unused callsign from the pool of available call signs appropriate for their license class.)
Generally, the shorter a ham's callsign, the greater his or her license rating and the greater his or her operating privileges, i.e. the number of frequencies he or she is allowed to use. (There are exceptions to this rule, for example, a ham may elect to retain his current callsign even if he earns a higher license class.)
When hams talk on the radio, they always identify themselves by their callsign, even before they mention their first name (last names are rarely used at all). This is primarily because callsign identification is required by international law, but it's also a handy way for hams to specify a particular operator since each callsign is unique. There is no confusion with a callsign as there would be if you had two or more operators named "Bob" on frequency.
A callsign also makes a handy identifier for hams who like to write down who they have spoken to on the radio, particularly for hams who are participating in contests (to see how many other hams they can contact in a short period of time;) or for hams who want to want to prove they have spoken to hams in many different countries (there are different awards for contacting 100 or more countries, or all the states or provinces in a country, or even all the counties in the US).
Callsigns can also be assigned to a radio stations or organizations, including:
- radio clubs
- special event stations (established by hams for a short time to commemorate some event, persons, etc.)
- government radio stations
- special purpose stations such as voice repeaters (radios which just instantaneously re-transmit signals directed to them -- to extend the range of a signal)
- and of course commercial radio and TV stations