Same HTML Signature for every device using my smtp?

Hi currently a user can send emails through my server's smtp, either from his mobile, pc, gmail any email client actually and the signature is not standard on all those email clients and devices. The reason is that the user is not able to create or duplicate the same signature I had created on his webmail to his devices.

My boss is asking me if we can create a standard HTML signature for every email account unique to the account but the same across all devices for that email account. How can this be possible? Is it actually? Any links to study?

 

Thank you I will have a look although I guess that is going to append a signature to all outgoing emails of all users on the server