A trademark is a legally registered or established identifier (name, word, symbol, design, or combination) representing a company or product. It legally prevents unauthorized usage.
Definitions:
Brand name: The spoken identifier of a brand (e.g., "Nike").
Brand mark: The visual identifier of a brand (e.g., the Nike swoosh).
Trademark: A brand name or mark with legal protection.
Logo: A graphic emblem used by a business (may be part of a trademark).
Therefore, the accurate legal designation is (C) Trademark.