CiviMail token for sender signature
Yes there is but it only works for regular mails not for mails sent by CiviMail (bulk mails):


Add signature to the CIviCRM contact that is connected to your CMS contact (see screenshot).
Click on send email for a contact and the signatures should be in the Text editor.


However, for Bulk Mails you would have to put the signature in a footer or th emessage template.