Wiktionary
n. (context broadcasting English) Term used to describe the closing of a radio or television station's studios and cessation of a broadcasting signal, usually during the overnight hours. vb. 1 (context idiomatic English) To log off; to stop using a computer, radio, etc., especially to stop talking. 2 (context broadcasting English) To cease broadcasting a radio or television signal, usually at the end of a broadcasting day. 3 (context followed by “on” English) to give one's official approval to something for which it is needed
WordNet
v. cease broadcasting; get off the air; as of radio stations
Usage examples of "sign off".
I'll want to see some contingency planning for a seizure of the ship, but, I'll tell you now that in all honesty I don't anticipate your being able to put together an option that I'll sign off on.
All it says is that you have to have a representative of the local government examine the cargo and sign off on it.
The Bureau of Personnel had to sign off on her nominees, but that was only a formality.
We're aware that your medical treatment shouldn't take much more than a year, however, and as soon as the medicos sign off for your return to full, active duty, we'll find a replacement.