Sign off may refer to any of the following:
1. Alternatively referred to as log, log off, and sign out, sign off is the process of disconnecting from a network or account voluntarily. For example, to check your credit card balance, you log into your account. When you are done reviewing the information, you log out, which is the same as signing off.
Why should I sign off of an account?
Computers and online services do not know who is sitting at your computer. If the service does not log you off automatically, you will remain online. If someone else was to get on a computer that you've used recently, they could access accounts and steal or change information contained within them.
Is it logout, log out, or log-out?
When spelled as one word, "logout" and "log-out" are a noun or adjective that describes the components required to sign out of an account. As two words, "log out" is a verb that describes the action of signing off of an account. For example, the sentence: "You need to log out with your logout information so no one else can read your e-mail." uses both forms of the word.
2. Finally, sign off is also a message commonly displayed when a user disconnects from a chat service. Most sign offs are witty quotes, sayings, or advertisements created by the user.