Idaho Code § 49-1427: Vehicles transporting explosives.

Any person operating a vehicle transporting any explosive as a cargo or part of a cargo, upon a highway, shall at all times comply with the provisions of this section.

(1) The vehicle shall be marked or placarded on each side and the rear with the word "explosives" in letters not less than eight (8) inches high, and there shall be displayed on the rear of the vehicle a red flag not less than twenty-four (24) inches square, marked with the word "danger" in white letters six (6) inches high.

(2) The vehicle shall be equipped with not less than two (2) fire extinguishers, filled and ready for immediate use, and placed at a convenient point on the vehicle.