Sign-off (or closedown) is the sequence of operations involved when a radio or television station shuts down its transmitters and goes off the air for a predetermined period; generally this occurs during the overnight hours. It is the opposite to a sign-on (or startup) which usually takes place at the start of the day.

Sign-offs, like sign-ons, vary from country to country, from station to station, and from time to time, however most follow a similar general pattern. Many stations follow the reverse process to their sign-on sequence at the start of the day. Sign-off messages can be initiated by a broadcast automation system just as for other television programming, and automatic transmission systems can cutoff the carrier signal and trigger the actual shutdown of the transmitter by remote control. Generally, after the carrier signal is cut, the viewer only sees or hears static.

Both sign-offs and sign-ons have become less common with the increasing prevalence of twenty-four hour a day, seven day a week broadcasting. They are, however, still conducted by a number of stations around the world, often by stations catering to small-markets or those in less developed countries, or when stations need to shut down for transmitter maintenance. Another consideration for whether providers shutdown is power consumption; aerial signals, such as those for UHF analog TV transmissions, can require tens of thousands of watts of power, making electricity a major expense, while power consumption would usually be considerably lower for cable and satellite providers.