You can use the use signature field to determine if every mail you send should be accompanied with your signature. A signature is useful to automatically insert additional information in every mail you send. You can use this field to either select the signature or disable it.
In the 'Mail Preferences' page, select the 'Use Signature' field to modify the signature settings. The options you have the settings are
Use e-mail signature : When you select this option, the signature from the signature field is attached at the end of every mail you send.
Don't use e-mail signature : When you select this option, the signature is not appended to the emails you send.