Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
stations or networks identifying themselves on air, typically by means of a call sign
In broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations...
or brand name (sometimes known, particularly in the United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, as a "sounder" or "stinger", more generally as a station or network ID). This may be to satisfy requirements of licensing authorities, a form of branding
The American Marketing Association defines a brand as a "Name, term, design, symbol, or any other feature that identifies one seller's good or service as distinct from those of other sellers."...
or a combination of both.