to give a final message at the end of a letter or when communicating by radio, or at the end of a television or radio programme

She signed off (her show) by wishing her listeners a Happy New Year. 她在结束播音时祝听众新年快乐。

to stop doing your work or a similar activity for a period of time

As it's Friday, I think I'll sign off early today. 今天是星期五，我想我会早点儿下班。

to report to a government employment office that you now have a job and do not need to receive benefit (= money paid by the government)