NFPA 72 isn't really specific as to what type use requires notification appliances other than "public mode" meaning that the fire alarm is for general evacuation. When such is the case, the audibility has to be met throughout the building or fire area that is required to have a fire alarm. Although NFPA 72 doesn't specify where the visible notification appliances have to be provided, most jurisdictions follow the ADA requirements, which require visible notification appliances in all toilets, hallways, lobbies and all other areas for general use. So, most jurisdictions require visible appliances in all areas except for private, individual offices. That being said, a cold storage room is no different than any other stock room or storage room with respect to the occupancy of the area, so it would normally require a visible notification appliance or appliances, depending on the size. I would require it in any storage room large enough to walk into and close the door.