sign

Concise Oxford English Dictionary © 2008 Oxford University Press:
sign/sʌɪn/

▶noun

• 1 an object, quality, or event whose presence or occurrence indicates the probable presence, occurrence, or advent of something else.

  ■ Medicine an indication of a disease detectable by a medical practitioner even if not apparent to the patient.

  Compare with symptom.

  ■ N. Amer. the trail of a wild animal.

• 2 a signal conveying information or an instruction.

  ■ a gesture used in sign language.

• 3 a public notice giving information or instructions in a written or symbolic form.

• 4 a symbol or word used to represent an operation, instruction, concept, or object in algebra, music, or other subjects.

• 5 Astrology each of the twelve equal sections into which the zodiac is divided, named from the constellations formerly situated in each, and associated with successive periods of the year according to the position of the sun on the ecliptic.

• 6 Mathematics the positiveness or negativeness of a quantity.

▶verb

• 1 write one's name on (something) for the purposes of identification or authorization.

  ■ write (one's name) for such a purpose.

• 2 (with reference to a sports player, musician, etc.) engage for or commit oneself to work by signing a contract.

• 3 use gestures to convey information or instructions.

  ■ communicate in sign language.

• 4 indicate with signposts or other markers.

• 5 mark or consecrate with the sign of the cross.

– phrasal verbs
sign in (or out) sign a register on arrival (or departure) in a hotel or workplace.
sign someone in (or out) record someone's arrival (or departure) in a register.
sign off conclude a letter, broadcast, or other message.

• 1 commit oneself to employment, membership of a society, etc.

• 2 Brit. register as unemployed.

sign someone on take someone into one's employment.
sign up

• 1 commit oneself to a period of employment, education, etc.

• 2 (also sign something up) conclude a business deal.

– derivatives
signable adjective,
signed adjective,
signer noun.

– origin ME: from OFr. signe (n.), signer (v.), from L. signum ‘mark, token’.