No person driving or in charge of a motor vehicle shall permit it to stand unattended without first stopping the engine, locking the ignition, removing the key and effectively setting the brake, or placing the transmission in parking position, thereon and, when standing upon any grade, turning the front wheels in such manner that the vehicle will be held by the curb or will leave the highway if the brake fails. A violation of this section shall not mitigate the offense of stealing a motor vehicle, nor shall the provisions of this section or any violation thereof be admissible as evidence in a civil action for the recovery of a stolen motor vehicle, or in any other civil action arising out of the theft of a motor vehicle.