The option to add a custom website signature can now be added easily in the General Settings section of the admin.

The "General" tab of the General Settings section can be used to add a signature for the default system emails. 

This section will only edit the default website emails. There is also an option to add a different signature for the admin operator in the admin settings. More information on this in the link below. 

Editing Admin Operators

FROALA Text Editor: Versions and their Upload Functionalities  

Froala Editor - Tables