(transitive, now rare) To seal (a document etc.) with an identifying seal or symbol. / (transitive) To mark, to put or leave a mark on.

(sometimes also used uncountably) A perceptible (e.g. visible) indication. / (Canada, US, Australia, uncountable) Physical evidence left by an animal.

The symbol @, most commonly used in e-mail addresses.

(idiomatic) To sign one's name on a list when entering a place, to indicate one's arrival. / (computing) To take some action to access a secured program or web page on a computer; to log in.

The username and password for logging in to a computer account. / An attempt to log in. / (more generally) An instance of signing on to something. / A person who signs on to something.

(broadcasting) The time of day when a radio or television station begins broadcasting, usually after being off the air for several hours. / Alternative form of sign-on

To join something, after signing. / To commit oneself, as to a project, a goal, an organization, a cause.

Alternative form of at sign

Having a signature; endorsed. / (mathematics, computer science) Having both positive and negative varieties. / (of a road, route) Furnished with signs and signposts; signposted.

simple past tense and past participle of sign