The exact extract asks for the types of safety signs and lists information, mandatory action, prohibition sign, and warning sign. The correct answer is A, B, C, D. Safety signs are designed to communicate hazards or required behavior quickly through standardized colors, geometric shapes, and symbols. Information signs provide safety-related guidance or location information, such as emergency exits or first-aid points. Mandatory action signs indicate an action that must be taken, such as wearing PPE or using insulated tools. Prohibition signs indicate actions that are not allowed, such as no smoking or no open flame. Warning signs indicate a hazard requiring caution, such as electrical danger, high voltage, hot surface, or battery risk. In PV and ESS projects, these signs are not decorative; they are part of site safety control, warehouse safety, electrical safety, and emergency response. Therefore, every listed category is a valid safety-sign type. Reference: Huawei HCSA-Sales-Smart PV V2.0 Safety Management training extract.