To exit a user account in a computer system, so that one is not recognized until signing in again.
The time of day when a radio or television station begins broadcasting, usually after being off the air for several hours.
To begin broadcasting a radio or television signal, usually at the beginning of a broadcasting day and after being off the air for several hours.
To commit oneself, as to a project, a goal, an organization, a cause.
To join something, after signing.
To apply to receive unemployment benefits.
To log on; to start using a computer, radio, etc., or to start talking.