I modified the Email Content RegEx to filter out our organizations default signature (which gets appended automatically when sending to external addresses, which our WHD monitored email account is)
(?s)[\r\n]{1,2}-- {1,2}[\r\n]{1,2}.*$|(?s)[\r\n]{1,2}Important -{1,2}.*$
It filters out after 'Important -'.
Could be better, but suits our setup.