While technically possible to insert at the server level its really far better to create a "Company Signature" and deploy this across every computer in the workplace and add it as new computer go into service.
While time consuming initially it has the advantage of working without problems which is a lot more than can be said for a Server Inserted Signature which if not properly installed will prevent all outgoing e-mail and there is always the possibility that the hole that you use to insert this could be plugged by a Patch which would make all your previous work useless and cripple the company e-mail until you could remove the server setting.
You should be able to create a signature file on the server and then go to each workstation and use your data file as a signature file on each workstation e-mail account.
Col