<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (August 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> Call signs are frequently still used by North American broadcast stations, in addition to amateur radio and other international radio stations that continue to identify by call signs around the world . Each country has a different set of patterns for its own call signs . Call signs are allocated to ham radio stations in Barbados, Canada, Mexico and across the United States . </P> <P> Many countries have specific conventions for classifying call signs by transmitter characteristics and location . The call sign format for radio and television call signs follows a number of conventions . All call signs begin with a prefix assigned by the International Telecommunications Union . For example, the United States has been assigned the following prefixes: "AAA"--"ALZ", "K", "N", "W". For a complete list, see international call sign allocations . </P> <P> Pertaining to their status as former or current colonies, all of the British West Indies islands shared the VS, ZB--ZJ, ZN--ZO, and ZQ prefixes . The current, largely post-independence, allocation list is as follows: </P>

What do the w and k stand for in call letters