Final answer:
In Brian's case, the fever is a sign of disease because it is an objective measurement. Nausea and migraine are symptoms since they are subjective experiences only Brian can feel and report.
Step-by-step explanation:
In the context of Brian's medical condition, signs are objective evidence of disease that can be measured or observed, while symptoms are subjective experiences reported by the patient. In Brian's case, the fever of 38 °C (100.4 °F) is a sign, as it is an objective measurement that can be verified independently of the patient's feelings. The complaint of nausea and the constant migraine, however, are considered symptoms because these are experiences that Brian feels and reports, and cannot be measured directly.