@Mahzad Sharifahmadian PhD MBA are the email templates using the account.name variable below sender.full_name. That might be why you think it is not updating. 

1. expand fundraising with the > in the left nav
2. click "LP Emails"
3. select a template
4. if you see account.name at the bottom do the following
5. delete the account.name 
6a. in the right side of the template writer (which is also available in individual emails) click "Variables" tab between "AI Assistant" and "Files"
6b. OR type {{sender.email_signature}} space bar and the variable will be recognized

Then when you go to send these templates it will be taking your created signature