sign

Etymology 1

From Middle English signe, sygne, syng, seine, sine, syne, from Old English seġn (“sign; mark; token”) and Old French signe, seing (“sign; mark; signature”); both from Latin signum (“a mark; sign; token”); root uncertain. Doublet of signum. Partially displaced native token.

noun

1. (sometimes also used uncountably) A fact that shows that something exists or may happen.
   Their angry expressions were a clear sign they didn't want to talk.
   Those clouds show signs of raining soon.
   Those clouds show little sign of raining soon.
   Signs of disease are objective, whereas symptoms are subjective.
2. A mark or another symbol used to represent something.
   The sharp sign indicates that the pitch of the note is raised a half step.
   I gave them a thumbs-up sign.
   The sound of the Orlando dinner train whistle reminds me that it ' s already Friday, an auditory sign. Another auditory sign, a distant thunder clap, warns me of limited computer time before our evening thunderstorm moves in. 2000, Geoffrey McGuinness, Carmen McGuinness, How to Increase Your Child's Verbal Intelligence: The Language Wise Method, Yale University Press, page 38
3. (Canada, US, Australia, uncountable) Physical evidence left by an animal.
   The hunters found deer sign at the end of the trail.
   Animal sign is the key to eliminating guesswork when setting your traps. Only trap where there is sign. Sign is anything the animal leaves as a trace that indicates it may have passed through the area. 2015, Dave Canterbury, Advanced Bushcraft: An Expert Field Guide to the Art of Wilderness Survival, page 127
4. A clearly visible object, generally flat, bearing a short message in words or pictures.
   The sign in the window advertised a room for rent.
   I missed the sign at the corner so I took the wrong turn.
5. A wonder; miracle; prodigy.
6. (astrology) An astrological sign.
   Your sign is Taurus? That's no surprise.
7. (mathematics) Positive or negative polarity, as denoted by the + or - sign.
   I got the magnitude right, but the sign was wrong.
8. A specific gesture or motion used to communicate by those with speaking or hearing difficulties; now specifically, a linguistic unit in sign language equivalent to word in spoken languages.
   In American Sign Language (ASL), for instance, the sign for 'catch' is formed with one hand (in the role of agent) moving across the body (an action) to grasp the forefinger of the other hand (the patient). 2007, Marcel Danesi, The Quest for Meaning
9. (uncountable) Sign language in general.
   Sorry, I don't know sign very well.
10. A semantic unit, something that conveys meaning or information (e.g. a word of written language); (linguistics, semiotics) a unit consisting of a signifier and a signified concept. (See sign (semiotics).)
    A Noun substantive and a Noun adjective may be thus distinguished, that a substantive may have the sign a or the before it; as, puer, a boy, the boy; but an adjective cannot, as, bonus, good. 1692, Thomas Bennet, Short Introduction of Grammar ... of the Latine Tongue
    A Pronoun is a Noun implying a Person, but not admitting the Sign a or the before it. 1753, Charles Davies, Busby's English Introduction to the Latin Tongue Examined, page 11
    And some linguistic signs, like “the”, “and” or “with”, may lack apparent objects, though they are clearly meaningful and interpretable. 2008, Eero Tarasti, Robert S. Hatten, A Sounding of Signs: Modalities and Moments in Music, Culture, and Philosophy : Essays in Honor of Eero Tarasti on His 60th Anniversary
11. An omen.
    "It's a sign of the end of the world," the doom prophet said.
12. (medicine) A property of the body that indicates a disease and, unlike a symptom, can be detected objectively by someone other than the patient.
13. A military emblem carried on a banner or standard.

Etymology 2

From Middle English signen, seinen, seinien, partly from Old English seġnian (“to mark; sign”) and partly from Anglo-Norman seigner, seiner et al., Old French signer et al., and their source Latin signāre (“to mark, seal, indicate, signify”); all from Latin signum (“a mark, sign”); see Etymology 1, above. Compare sain.

verb

1. To make a mark
   1. (transitive, now rare) To seal (a document etc.) with an identifying seal or symbol.
      The Queen signed her letter with the regal signet.
   2. (transitive) To mark, to put or leave a mark on.
      Meantime revolving in his thoughtful mind / The scar, with which his manly knee was sign'd […]. 1726, Elijah Fenton, The Odyssey of Homer
   3. (transitive) To validate or ratify (a document) by writing one's signature on it.
   4. (transitive) More generally, to write one's signature on (something) as a means of identification etc.
      I forgot to sign that letter to my aunt.
   5. (transitive or reflexive) To write (one's name) as a signature.
      Just sign your name at the bottom there.
      I received a letter from some woman who signs herself ‘Mrs Trellis’.
   6. (intransitive) To write one's signature.
      Please sign on the dotted line.
   7. (intransitive) To finalise a contractual agreement to work for a given sports team, record label etc.
      Agents say Wales back Gavin Henson has signed for Cardiff Blues. 2011, The Guardian, (headline), 18 Oct 2011
   8. (transitive) To engage (a sports player, musician etc.) in a contract.
      It was a great month. I managed to sign three major players.
2. To make the sign of the cross
   1. (transitive) To bless (someone or something) with the sign of the cross; to mark with the sign of the cross.
      At the baptismal ceremony the child was […] signed with the cross in holy water. 1971, Keith Thomas, Religion and the Decline of Magic, Folio Society, published 2012, page 34
   2. (reflexive) To cross oneself.
      Shaking a fist at him with one fierce arm, / Signing himself with the other because of Christ. 1855, Robert Browning, Men and Women
3. To indicate
   1. (intransitive) To communicate using a gesture or signal.
   2. (transitive) To communicate or make known (a meaning, intention, etc.) by a sign.
   3. (transitive) To communicate using gestures to (someone).
      He signed me that I should follow him through the doorway.
   4. (intransitive) To use sign language.
   5. (transitive) To furnish (a road etc.) with signs.
4. To determine the sign of
   1. (transitive) To calculate or derive whether a quantity has a positive or negative sign.