All about the comma sign on aircraft engines
Some think it is for scaring birds away when the aircraft is in flight! In fact, this endless swirl is really there for safety reasons once the aircraft is on the ground.
As it turns, the spiral signals that the jet engine is running. When spinning, this symbol warns teams on the ground – who often work very close to the aircraft – to stand well away to avoid getting sucked into the turbofan.
Workers on the ground near a Boeing 737 engine running slowly have to stay at least three meters away from the front and sides of the aircraft to not risk getting swept off their feet by the turbofan. When the engine is running at full power, the danger zone is extended to five meters minimum, or even more depending on the type of aircraft.