[MezzoDelCammin]

not a spark plug. They call it "armature in a circle", but that's somewhat generic.

Bosch used to do the first magnetos / dynamos in the early 1900s motorbikes / cars. The principle is similar to this day - one rotating magnetic field within one static. You can do all kinds of shenanigans and combinations of permanent magnets / coils where it's either the electric current generating a magnetic field or the magnetic field generating an electric current. Depending whether You want the movement to generate electricity or the electricity to generate movement.

In the first magnetos (the thing that uses the engine rotation in order to generate a current that then makes a spark in the spark plug) they used permanently magnetized exterior plating and a rotating winding. That's sort of what You see in the logo - two coil windings rotating in their housing.