Is there a token for email sender's signature?
I need the email generated from template to be signed by the person who is sending the email.
Yes there is but it only works for regular mails not for mails sent by CiviMail (bulk mails):
However, for Bulk Mails you would have to put the signature in a footer or th emessage template.
You might find the code in https://github.com/JMAConsulting/biz.jmaconsulting.sigs a useful starting place for a token for CiviMail - a PR for this would be welcome. Feel free to contact me if you would like us to develop it for you.