The Collaborative International Dictionary of English v.0.48:

Signify \Sig"ni*fy\, v. t. [imp. & p. p. Signified; p. pr. &
   vb. n. Signifying.] [F. signifier, L. significare; signum a
   sign + -ficare (in comp.) to make. See Sign, n., and
   -fy.]
   1. To show by a sign; to communicate by any conventional
      token, as words, gestures, signals, or the like; to
      announce; to make known; to declare; to express; as, a
      signified his desire to be present.
      [1913 Webster]

            I 'll to the king; and signify to him
            That thus I have resign'd my charge to you. --Shak.
      [1913 Webster]

            The government should signify to the Protestants of
            Ireland that want of silver is not to be remedied.
                                                  --Swift.
      [1913 Webster]

   2. To mean; to import; to denote; to betoken.
      [1913 Webster]

            He bade her tell him what it signified. --Chaucer.
      [1913 Webster]

            A tale
            Told by an idiot, full of sound and fury,
            Signifying nothing.                   --Shak.
      [1913 Webster]

   Note: Signify is often used impersonally; as, it signifies
         nothing, it does not signify, that is, it is of no
         importance.
         [1913 Webster]

   Syn: To express; manifest; declare; utter; intimate; betoken;
        denote; imply; mean.
        [1913 Webster]

WordNet (r) 3.0 (2006):

signify
    v 1: denote or connote; "`maison' means `house' in French"; "An
         example sentence would show what this word means" [syn:
         mean, intend, signify, stand for]
    2: convey or express a meaning; "These words mean nothing to
       me!"; "What does his strange behavior signify?"
    3: make known with a word or signal; "He signified his wish to
       pay the bill for our meal"

Moby Thesaurus II by Grady Ward, 1.0:

115 Moby Thesaurus words for "signify":
   add up to, amount to something, announce, approve, argue, assign,
   attest, augur, be construed as, be featured, be indicative of,
   be prominent, be significant of, be somebody, be something,
   be symptomatic of, bear, bespeak, betoken, breathe, carry,
   carry weight, characterize, communicate, connote, convey, count,
   cut ice, cut some ice, declare, demonstrate, denominate, denote,
   designate, determine, differentiate, disclose, display, divine,
   entail, evidence, evince, exhibit, express, fix, foretoken,
   furnish evidence, get top billing, give evidence,
   give indication of, give token, go to show, highlight, hint,
   identify, illustrate, impart, imply, import, impress, indicate,
   intend, intimate, involve, make known, manifest, mark, matter,
   mean, mention, name, note, pick out, pin down, point out, point to,
   prefigure, preindicate, presign, presignal, presignify, pretypify,
   purport, refer to, represent, reveal, say, select, set, set forth,
   show, show signs of, sign, signal, signalize, speak for itself,
   speak volumes, specialize, specify, spell, stand for, stand out,
   star, state, stipulate, suggest, symbolize, symptomatize,
   symptomize, tell, tend to show, testify, token, typify, weigh