sign

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Something that suggests the presence or existence of a fact, condition, or quality.
• noun An act or gesture used to convey an idea, a desire, information, or a command: synonym: gesture.
• noun Sign language.
• noun A displayed structure bearing lettering or symbols, used to identify or advertise a place of business.
• noun A posted notice bearing a designation, direction, or command.
• noun A conventional figure or device that stands for a word, phrase, or operation; a symbol, as in mathematics or in musical notation.
• noun An indicator, such as a dropping or footprint, of the trail of an animal.
• noun A trace or vestige.
• noun A portentous incident or event; a presage.
• noun Medicine An objective finding, usually detected on physical examination, from a laboratory test, or on an x-ray, that indicates the presence of abnormality or disease.
• noun One of the 12 divisions of the zodiac, each named for a constellation and represented by a symbol.
• intransitive verb To affix one's signature to.
• intransitive verb To write (one's signature).
• intransitive verb To approve or ratify (a document) by affixing a signature, seal, or other mark.
• intransitive verb To hire or engage by obtaining a signature on a contract.
• intransitive verb To relinquish or transfer title to by signature.
• intransitive verb To provide with a sign or signs.
• intransitive verb To communicate with a sign or signs.
• intransitive verb To express (a word or thought, for example) by sign language.
• intransitive verb To consecrate with the sign of the cross.
• intransitive verb To make a sign or signs; signal.
• intransitive verb To use sign language.
• intransitive verb To write one's signature.

from The Century Dictionary.

• To mark with a sign, either fixed or (as by a significant motion) passing; place a sign or distinguishing mark upon; mark; specifically, to sign with the cross. Compare sain.
• To affix a signature to, as a writing of any kind, a design or painting, or the like, for verification, attestation, or assent; write one's name upon, or something intended to represent one's name, or (as by authorization or assumption) that of another person: as, to sign bills or receipts with the employer's name and the writer's initials; the plans were signed with a monogram.
• To write as a signature: as, to sign one's own or another's name to a letter.
• To affect by a binding signature; dispose of by written assignment or release: with away or off: as, to sign away one's rights; to sign off one's interest in a contract.
• To procure the signature of, as to an agreement; engage by the signing of a contract; put under written obligation.
• To communicate by a sign; make known by a significant motion; signal, as with the hand.
• To give or show signs of; display in appearance or manner; betoken or distinguish by any indication.
• To assign, as to a place or duty; direct; appoint; settle; fix.
• To write one's signature; bind one's self by a signature; make a signed agreement or statement: with an adverbial adjunct: as, to sign off from drinking (that is, to sign the temperance pledge).
• To serve as a sign; have significance; augur.
• To mate a sign or signs; gesture or point significantly.
• noun In geometry, the symbol .
• noun Avisible mark or impress, whether natural or artificial, accidental or purposed, serving to convey information, suggest an idea, or assist inference; a distinctive guiding indication to the eye.
• noun An arbitrary or conventional mark used as an abbreviation for a known meaning; a figure written technically instead of the word or words which it represents, according to prescription or usage: as, mathematical, astronomical, medical, botanical, or musical signs; occult signs; an artist's sign.
• noun Something displayed to announce the presence of any one; a cognizance; a standard; a banner.
• noun An inscribed board, plate, or space, or a symbolical representation or figure, serving for guidance or information, as on or before a place of business or of public resort, or along a road: as, a merchant's or shopman's sign; a tavern -sign; a swinging sign; a tin sign; a sign-board.