n. & v.
1 a a thing indicating or suggesting a quality or state etc.; a thing perceived as indicating a future state or occurrence (violence is a sign of weakness; shows all the signs of decay). b a miracle evidencing supernatural power; a portent (did signs and wonders).
2 a a mark, symbol, or device used to represent something or to distinguish the thing on which it is put (marked the jar with a sign). b a technical symbol used in algebra, music, etc. (a minus sign; a repeat sign).
3 a gesture or action used to convey information, an order, request, etc. (gave him a sign to leave; conversed by signs).
4 a publicly displayed board etc. giving information; a signboard or signpost.
5 any objective evidence of a disease, usu. specified (Babinski's sign).
6 a password (advanced and gave the sign).
7 any of the twelve divisions of the zodiac, named from the constellations formerly situated in them (the sign of Cancer).
8 US the trail of a wild animal.
9 Math. etc. the positiveness or negativeness of a quantity.
1 tr. a (also absol.) write (one's name, initials, etc.) on a document etc. indicating that one has authorized it. b write one's name etc. on (a document) as authorization.
2 intr. & tr. communicate by gesture (signed to me to come; signed their assent).
3 tr. & intr. engage or be engaged by signing a contract etc. (see also sign on, sign up).
4 tr. mark with a sign (esp. with the sign of the cross in baptism).
Phrases and idioms:
make no sign seem unconscious; not protest. sign and countersign secret words etc. used as passwords. sign away convey (one's right, property, etc.) by signing a deed etc. sign for acknowledge receipt of by signing. sign language a system of communication by visual gestures, used esp. by the deaf. sign of the cross a Christian sign made in blessing or prayer, by tracing a cross from the forehead to the chest and to each shoulder, or in the air. sign off
1 end work, broadcasting, a letter, etc., esp. by writing or speaking one's name.
2 a end a period of employment, contract, etc. b end the period of employment or contract of (a person).
3 Brit. stop receiving unemployment benefit after finding work.
4 Bridge indicate by a conventional bid that one is seeking to end the bidding. sign-off n. Bridge such a bid. sign of the times a portent etc. showing a likely trend.
sign on
1 agree to a contract, employment, etc.
2 begin work, broadcasting, etc., esp. by writing or announcing one's name.
3 employ (a person).
4 Brit. register as unemployed. sign-painter (or -writer) a person who paints signboards etc.
sign up
1 engage or employ (a person).
2 enlist in the armed forces.
3 a commit (another person or oneself) by signing etc. (signed you up for dinner). b enrol (signed up for evening classes).
signable adj. signer n.
Etymology: ME f. OF signe, signer f. L signum, signare

Useful english dictionary. 2012.