All Filemail users can change their default signature. Having a signature works the same way as it does on your phone or on any other e-mail client you use. The signature is inserted automatically into the message field of all new e-mails that you send through Filemail. You are free to delete or modify it after it is added to your message by default.
To set up your own signature, follow these steps:
Login to your account
Go to "Settings" and "My profile"
Find the "Default Settings" at the bottom.
Edit the "Signature" field