Final answer:
The label on a roast to be stored in the refrigerator must include the expiration date to ensure food safety by indicating when the meat is no longer safe to consume.
Step-by-step explanation:
When labeling a roast to be stored in the refrigerator, the most critical element to include on the label is the expiration date. This date informs users of the safe time frame within which the meat can be consumed. In contrast, the chef's signature, cooking method, and caloric content are not as essential for food safety as the expiration date, which is directly related to preventing foodborne illnesses by indicating when the meat should no longer be eaten. Therefore, the correct answer to the question is C. Expiration date.