What is Beacon?

Legal Definition
A beacon is an intentionally conspicuous device designed to attract attention to a specific location.

Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form of optical telegraphy.
-- Wikipedia
Legal Definition
A signal erected as a sea mark for the use of mariners; also, to give warning of the approach of an enemy. 1 Com. Dig. 259; 5 Com. Dig. 173.
-- Bouviers Law Dictionary
Legal Definition
A light-house or sca-mark, formerly used to alarm the country, in case of the approach of an enemy, but how used for the guidance of ships at sea, by night, as well as by day.
-- Black's Law Dictionary