There are several simple methods that can be used to identify the (Scientific) North and South poles of neodymium magnets.
1)The easiest way is to use another magnet that is already marked. The North pole of the marked magnet will be attracted to the South pole of the unmarked magnet.
2)If you take an even number of magnets and pinch a string in the middle of the stack and dangle the magnets so they can freely rotate on the string, the North pole of the magnets will eventually settle pointing North. This actually contradicts the “opposites attract” rule of magnetism, but the naming convention of the poles is a carry over from the old days when the poles were called the “North-seeking” and “South-seeking” poles. These were shortened over time to the “North” and “South” poles that we know them as.
3)If you have a compass handy, the end of the needle that normally points North will be attracted to the North pole of the neodymium magnet.
4)Use Pole Identifier Devices.
(Please note: In some magnetic therapy applications, the definitions of the poles are reversed from the scientific definition described above. Please be sure to confirm the proper definition of the poles prior to using magnets for medical purposes)