If you have a lot of users and you want to control their email signature, then signature template is what you need. With my module res_users_signature you can create signature template and apply one for your users.

A user can choose his signature template himself at Preference window (which is opened via top right hand menu).

Technically the module make minimal changes at user model. It just put new value to signature field at res.users model.

The module updates signature if there are changes at basic users models (res.users, res.partner, hr.employee). E.g. if a user change his phone number, then his signature would be updated. Also, you can update all signatures manually.

Images

You can use base64-encoded images at signature template: 

<img src="data:image/png;base64,${user.company_id.logo_web}"/>
<img src="data:image/png;base64,ABCDE....12345="/>

I've found, that some email clients doesn't show such images. In order to fix it, the module overwrite build_email function at ir.mail_server model. The module make attachments from base64 images at email body. 

class ir_mail_server(models.Model):
    _inherit = "ir.mail_server"

    def build_email(self, email_from, email_to, subject, body, email_cc=None, email_bcc=None, reply_to=False,
               attachments=None, message_id=None, references=None, object_id=False, subtype='plain', headers=None,
               body_alternative=None, subtype_alternative='plain'):
        """ copy-pasted from openerp/addons/base/ir/ir_mail_server.py::build_email """

        ftemplate = '__image-%s__'
        fcounter = 0
        attachments = attachments or []

        pattern = re.compile(r'"data:image/png;base64,[^"]*"')
        pos = 0
        new_body = ''
        while True:
            match = pattern.search(body, pos)
            if not match:
                break
            s = match.start()
            e = match.end()
            data = body[s+len('"data:image/png;base64,'):e-1]
            new_body += body[pos:s]

            fname = ftemplate % fcounter
            fcounter += 1
            attachments.append( (fname, base64.b64decode(data)) )

            new_body += '"cid:%s"' % fname
            pos = e

        new_body += body[pos:]
        body = new_body

        //...

Repository: https://github.com/yelizariev/addons-yelizariev/tree/8.0/res\_users\_signature