this is the first time I've heard of the Rotosphere, since I didn't grow up in big cities, and they are rare to find after the 80s

Approximately 234 were built from 1960-1971. Only about 20 Roto-Spheres are left with maybe 4 being fully operational

They were created and produced by Warren Milks who made approximately 234 of them at his sign shop in Bossier City, LA.

Roto-Spheres feature sixteen aluminum spikes outlined in neon. These multi-colored spikes are each eight feet long. They are mounted on a ball that spins in three directions. Not only does the sign rotate on its pole, but the ball itself is composed of two counter-rotating hemispheres. A motor and three gears resembling an automobile's rear axle differential are used to power the ball.

https://www.roadarch.com/08/3/roto-sphere_patent.pdf https://www.roadarch.com/sca/roto.html