I agree
although I would use the term :" banner stone".
It is used on a spear shaft to add heft/weight to the spear to assure a deeper puncture to the hunted animal.
A projectile point on the tip of an unweighted spear might not even puncture the animal hide,
but just create a superficial wound and bounce off.
Banner stones were mounted on the Atlatyl shaft, not the projectile Dart shaft.
This does not look even remotely like a bannerstone.
Banner stones (as opposed to other types of nonperforated atlatl weights such as are seen out in the Southwest) were used in Eastern North America where whitetail deer in heavy cover (as opposed to the more open country of mule deer) were the choice prey, and not so much to make the spear go deeper or more forcefully as to steady the throwing arm of the hunter as he waited in position to make the throw. There has been a very good study of this benefit of the bannerstone conducted by live measured experiments in the St. Louis area. The weight of the stone steadied the atlatl-bearing arm and dramatically reduced strain and muscle tremor, enabling the throwers to remain comfortably in position quite a long time before the deer could spot them. This was very practical for white tails in their forested habitat, which would be alerted to anyone trying to get their atlatl in position to throw after spotting the deer.