Why do emails include two signatures?
Businesses want a consistent brand identity. When sending emails, this may include a uniform signature (in addition to an organization-wide sender address). This is why you usually include an email signature in the Email Body or Email HTML Body field when defining your email text.
If users who trigger the email distribution have configured a signature in their personal email settings, the outgoing emails will include the two signatures: the one from the template and the user's personal signature – irrespective of whether an org-wide sender address is enabled.
How to prevent that?
To have JustOn use only the signature specified in the template, you can disable the user signature. To this end, you select the checkbox Disable Global Email Signature on the relevant template.
Info
You may have to first add the checkbox field Disable Global Email Signature to the template layout. For help about modifying page layouts, see Managing Pages.
Related information:
Modifying Invoice Email
How to use an organization-wide email sender address?
Managing Pages
Edit Your Email Settings in the Salesforce Help