simple past tense and past participle of sign on

present participle of sign on

simple past tense and past participle of sign in

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

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

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

present participle of 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

(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.