This is a confusing question, with conflicting answers listed across the Internet. The following methods will indicate the poles as defined within the magnetic sensing industry. 1.) Use a compass: The south pole of a magnet will attract the end of the compass needle pointing north. 2.) Float the magnet in still water, the north pole of the magnet will align with the magnetic north. 3.) Opposites attract, use a magnet with known poles, the marked north will attract the south pole of the unknown magnet. 4.) Purchase your magnets from Sensor Solutions, the south pole is labeled on the magnet or defined on the specifications sheet for potted magnets.