Source : Webster's Revised Unabridged Dictionary (1913)

   Note: Watches are often distinguished by the kind of
         escapement used, as an {anchor watch}, a {lever watch},
         a {chronometer watch}, etc. (see the Note under
         {Escapement}, n., 3); also, by the kind of case, as a
         {gold} or {silver watch}, an {open-faced watch}, a
         {hunting watch}, or {hunter}, etc.

   6. (Naut.)
      (a) An allotted portion of time, usually four hour for
          standing watch, or being on deck ready for duty. Cf.
          {Dogwatch}.
      (b) That part, usually one half, of the officers and crew,
          who together attend to the working of a vessel for an
          allotted time, usually four hours. The watches are
          designated as the {port watch}, and the {starboard
          watch}.

   {Anchor watch} (Naut.), a detail of one or more men who keep
      watch on deck when a vessel is at anchor.

   {To be on the watch}, to be looking steadily for some event.
      

   {Watch and ward} (Law), the charge or care of certain
      officers to keep a watch by night and a guard by day in
      towns, cities, and other districts, for the preservation
      of the public peace. --Wharton. --Burrill.

   {Watch and watch} (Naut.), the regular alternation in being
      on watch and off watch of the two watches into which a
      ship's crew is commonly divided.

   {Watch barrel}, the brass box in a watch, containing the
      mainspring.

   {Watch bell} (Naut.), a bell struck when the half-hour glass
      is run out, or at the end of each half hour. --Craig.

   {Watch bill} (Naut.), a list of the officers and crew of a
      ship as divided into watches, with their stations.
      --Totten.

   {Watch case}, the case, or outside covering, of a watch;
      also, a case for holding a watch, or in which it is kept.
      

   {Watch chain}. Same as {watch guard}, below.

   {Watch clock}, a watchman's clock; see under {Watchman}.

   {Watch fire}, a fire lighted at night, as a signal, or for
      the use of a watch or guard.

   {Watch glass}.
      (a) A concavo-convex glass for covering the face, or dial,
          of a watch; -- also called {watch crystal}.
      (b) (Naut.) A half-hour glass used to measure the time of
          a watch on deck.

Source : WordNet®

watch fire
     n : a fire lighted at night as a signal