Which signature format is correct for a provider's name in a business letter?

The correct format for a provider's name in a business letter is "Mary Smith, M.D." This format follows the professional and conventional standard used in formal correspondence. Including the full name followed by the appropriate degree—such as M.D. (Doctor of Medicine)—provides clarity on the qualifications of the provider. The comma before the degree is important in this format, as it separates the name from the title, making it easier for the reader to identify the person's name and credentials.

Other options either use abbreviations or do not follow the standard punctuation rules associated with professional qualifications. For instance, using "Dr." along with the last name or referring to the individual as "Mrs." would not align with the formal and neutral manner often preferred in business letters, especially in a medical context where professionalism is key. Using "M.D." without a comma also does not conform to the typical style guide recommendation for such signatures.