Call sign

From AB9RF

A call sign is a moderately short sequence of letters and numbers that more or less uniquely identifies each ham radio operator. Call signs are normally assigned by the government agency that regulates amateur radio in whatever country the ham is operating. Operating regulations require hams to identify with their call sign on a regular basis during communications, although the details of this vary from country to country as well.

The use and structure of ham call signs is controlled by international treaty, because radio signals can and do travel worldwide. Each country has one or more prefixes assigned to it; the full list of prefixes is long and changes occasionally as new countries come into the treaty or unused combinations are assigned to countries that need more. Ham call signs start with a prefix appropriate for the country of licensure, followed in almost all cases by a single digit and then typically one to four more letters.