Rules can be configured to apply to all users or you can limit the scope of senders using various criteria.
Use the Azure AD field filter if you want a signature to be added to an email only if the sender matches very specific crietria.
In the Design tab, you can access the signature template editor and then preview the signature template designed for the rule.
CodeTwo Email Signatures for Office 365 comes with a WYSIWYG editor, which lets you easily design email signature templates in HTML, RTF and Plain text formats.
The program automatically integrates with your Office 365 tenant - no manual configuration is needed.