What the heck is this thing for and why is it even there? Often seen on higher-end, fixed blade knives as a custom touch. You've seen them and scratched your head or probably have a knife of your own with a notch or two at the base of the blade just aft of the sharpened edge and just ahead of the handle or guard. But why? Well... there are actually many theories and we're going to lay them out for you so you can decide.
1) They are decorative and actually pretty hard to get onto the blade well. So it can be an artistic touch used by blade makers to show off their skills.
2) The small 'U' in the notch can be used to thin sinew to make it more usable as a thread in the field. This had been used in the past, especially the Old West.
3) Another historical reason is the size of the notch. Older versions corresponded in size to a percussion cap nipple allowing for easy removal during the muzzle loading era.
4) If sized right, it can be used effectively as a fire strike area against the proper sized ferrous rod. You don't have to ruin your precious edge or disfigure the spine, plus it locked it in place for accurate striking.
5) If you did need to use your blade for fighting or self-defense, the notch can disrupt or even catch your opponent’s blade, making a counter easier.
6) Lastly as a blood catch. While hunting (or fighting) you may get a lot of blood on your blade and the notch held up the flow and allowed the blood to drip off at that point keeping it from your hand and grip area. No slippery handle here.
So you can see all of the above probably had their place at one time or another. We leave it to you to decide the overriding reason for that little curious, yet attractive accent you see on your own knife.