can you determine if a case was created by a case creation rule, or through an outlook plugin "convert-to-case"?

Hello,

I would like to know if there is some hidden flag that indicates how a case was created.  I would like to distinguish between cases created in the web application, cases created by incoming email in the "Case Creation Rule" and cases created by tracking/convert to case in Outlook.  Is there any flag or field that indicates the method of the case creation?

Version: 8.2 On-Premises, using Email Router