LEFT AND RIGHT EARPHONE

I've used headphone everyday for about 15 year but I just recently noticed a neat trick. I listen to books on tape every night, most of the time I've cut off all the light before putting them in my ear. I noticed a nub or dot on only one earphone. I turned the light on and noticed it was the left ear. Well I only listen on one side....the left. How cool is this. I use the type in the picture. Not all sets have this identifying "dot". For someone with poor vision I'm always looking for things to make life easier by using my sense of touch instead of relying on my vision.