Years ago someone invented something to place on the tops of antennas
that improved their signals considerably. The military allegedly
purchased many of these. They looked like a ball with a tear-drop
shape where the small pointed end fit over the end of the antenna.

Is this that same device or something along it's principal?

Same thing basically...But it ain't gonna improve the signal. At all...
It's not large enough to act as much of a capacity hat....
Might lower received static noise though, compared to a
sharp tip...That would vary also, to the climate, humidity, etc...
Most of my "stinger" whips start out with a small ball...But after
a week, I've usually whacked it off, hitting trees...I don't bother
to replace...
MK