User Configuration > Administrative Templates > Microsoft Word 2016
User
HKCU\software\policies\microsoft\office\16.0\word\options
This policy setting allows you to control whether users can request eSignatures directly from Word in tenants that have enabled Microsoft's native eSignature service. If you enable this policy setting, users can request eSignatures from within Word. This policy setting applies only to subscription versions of Word. If you disable this policy setting, users cannot request eSignatures from within Word. If you don't configure this policy setting, users cannot request eSignatures from within Word.