Test if ItemSend was Triggered by a Rule

I am currently working out of my usual office and have my PC setup to run and forward most emails to my out of office address via a Rule.
However, the office implemented a policy that requires job numbers in the subject of all outgoing emails. So I had created an ItemSend procedure to flag messages with subjects that are missing job numbers. So my rule fails to actually send the emails, unless they have job numbers.
So my question is this: Is there a way in my procedure to tell if the ItemSend was the result of a rule, vs someone manually hitting a Send or Forward?
TIA