A signature is short text that is included at the bottom of your outgoing email messages. You can define what you want to include, for example, your name, position, phone number, address, and anything else you always want to send. You can set up your signature in Mail Options. You can disable it without deleting it.
The signature text is included as soon as the Compose window is opened, so you can change it or delete it for the current message before sending.