46 C.F.R. § 35.40-10
Steam, foam, carbon dioxide, or clean agent fire smothering apparatus—TB/ALL
Each steam, foam, carbon dioxide, or clean agent fire fighting apparatus must be marked “[CARBON DIOXIDE/STEAM/FOAM/CLEAN AGENT—as appropriate] FIRE APPARATUS” in red letters at least 2 inches high. Branch pipe valves leading to the several compartments must be distinctly marked to indicate the compartments or parts of the vessel to which they lead.