Signs with chasing lights had a drum and electric motor that turned the drum.
So then that _IS_ how they work?!?!
When I was a kid I'd stand under the metal awnings of some grocery stores with chasing lights around the rim and I'd hear a constant mechanical whir-whirr clank clank in rythm with the lights.
I always thought it would be something similar to what you described
Are these devices still made or have they been replaced by some sort of solid-state thing?