To log off; to stop using a computer, radio, etc.; especially, to stop talking.
sign on
To log on; to start using a computer, radio, or other multicast device…
shut one's mouth
To stop talking; to be quiet.
shut one's face
drop the topic
To stop talking about the topic at hand.
shut one's trap
put a sock in it
To stop talking; to be quiet; to shut one's mouth.