This read-write INTEGER (enable(1)/disable(2)) controls, per its source description, whether sequence numbers are displayed in syslog output messages. Admins enable this to make it easier to detect gaps or dropped messages in a syslog stream, since each message carries an increasing sequence number that a log-collection tool can check for continuity. For example, enabling sequence numbers would let a log-monitoring script detect a jump from sequence 105 to 108 as evidence that three messages were lost in transit.