Why do some engines have commas?
The next time you notice a comma or a spiral or a swirl on the aircraft engine, do not take it to be a design element. In fact, those signals are single-handedly responsible for saving a lot of lives.
Simply put, the design is a cue for on-ground staff to stay away from the engine. It works like this: the symbol in motion signals the staff that the engine is running. It is said that when the engine is on idle speed, it has a hazard area of 9 ft to both, the front and sides of the engine.