def _tracking_code(self, course_key, cert_mode, target):
        """Create a tracking code for the button.

        Tracking codes are used by LinkedIn to collect
        analytics about certifications users are adding
        to their profiles.

        The tracking code format is:
            &trk=[partner name]-[certificate type]-[date]-[target field]

        In our case, we're sending:
            &trk=edx-{COURSE ID}_{COURSE MODE}-{TARGET}

        If no partner code is configured, then this will
        return None, indicating that tracking codes are disabled.

        Arguments:

            course_key (CourseKey): The identifier for the course.
            cert_mode (str): The enrollment mode for the course.
            target (str): Identifier for where the button is located.

        Returns:
            unicode or None

        """
        return (
            u"{partner}-{course_key}_{cert_mode}-{target}".format(
                partner=self.trk_partner_name,
                course_key=unicode(course_key),
                cert_mode=cert_mode,
                target=target
            )
            if self.trk_partner_name else None
        )