A fog signal station is a station at which a fog signal exists, but at which there is no lighthouse. A light tower might be appended to the station at a later date, as happened at The Cuckolds Light in Maine. A number of these stations were constructed along the California coast, although few survive in their original form.
See also Fiddler's Reach Fog Signal Lime Point Light Manana Island Sound Signal Station
References
under "Manana Island Fog Signal Station" Front matter, page 1.