Final answer:
A fever of 102.4°F is considered a sign because it can be measured. Inability to sleep, sore throat, and muscle aches can be symptoms.
Step-by-step explanation:
A sign refers to an objective indication of a disease or condition that can be observed or measured by healthcare professionals. Out of the given options, a fever of 102.4°F is considered a sign because it can be measured using a thermometer. Inability to sleep, sore throat, and muscle aches can all be symptoms, which are subjective experiences reported by the patient.