This depends on whether you have a Gmail or Outlook account.
Gmail or Google Workspace
As Campaigns directly integrates with your Gmail or Google Workspace account, the email signature is automatically retrieved from it.
The signature can be edited in your Gmail settings.
Outlook or Microsoft 365 Business
As the signature cannot automatically be retrieved from your Outlook or Microsoft 365 Business account, you will need to add it manually to the content of your emails and campaigns in Hunter.