Vehicles under the care and custody of the commission and used primarily in the detection and investigation of criminal violations of state and federal environmental laws are exempt from bearing the inscription required by Transportation Code, §721.002. The purpose of this exemption is to is to increase the effectiveness of commission investigators in detecting and investigating criminal violations of state and federal environmental laws, thereby allowing investigative personnel to accomplish their tasks undetected and to provide a greater degree of safety for these investigators, the state property being used in the investigation, and a greater degree of case integrity.