Corporate, government, academic and non-profit users often require all their users to use a common template for their signature, in accordance with their graphical identity. It would be very convenient for those entities and their individual users to have this template set by defaut so they may spend the least effort to set up email signatures on their new accounts.

A template signature could include any html design with the organisation logo, chosen font, etc, and blank fields to the individual user's name, position title, phone number, etc.

This could take the form of a default signature automatically appearing for all users, or a button in the "identity" creation menu that changes the signature field to the default signature set by an administrator account, or something else I haven't thought of.