Menuki are the good luck charms that are bound into the Ito of the Tsuka.
So if you look at the handle of your sword you will see one upon each side, they are chosen along with the furniture of the sword, like a Tsuba’s emblem or the Kashira’s pattern.
They can appear to a modern student a somewhat frivolous distraction from the serious business of warriorship in those days of old, but ornamentations, ritual and even superstition became very relevant when your life was frequently short and bloody, and was often very arbitrary as to who survived and who perished!
Much of our modern life now, seems to be so much in control, with our ordered societies with their healthcare, law and order, education etc. but control of one’s future can often just be an illusion, the student of philosophy understands that there is only one true reality, and that is the present moment! The sword student too should understand that despite all of the strategy, and all of their plans and techniques they may think they know, when two swordsmen meet it can all go array in the first clash of sword or Bokken!
Or as a the Samurai might of seen it:
“One thought of victory and you loose the real while clutching the false, so what is real? When the blades of your enemies are slashing ferociously at you, and your life hangs in the balance, you will know. If you do not, you have lived your life in vain.”
So let us forgive all human beings their desire for luck, for sometimes it is all we have!