Source : Webster's Revised Unabridged Dictionary (1913)

Signal \Sig"nal\, v. t. [imp. & p. p. {Signaled or Signalled};
   p. pr. & vb. n. {Signaling} or {Signalling}.]
   1. To communicate by signals; as, to signal orders.

   2. To notify by a signals; to make a signal or signals to;
      as, to signal a fleet to anchor. --M. Arnold.