Why do jet engines have spirals?

When boarding an airliner, have you looked at the jet engine and wondered why they have a spiral painted on the spinner?

Is it just for looks or not?

There are actually a few reasons, and they all have to with safety.

The primary function of the spiral is to warn the ground crew working around the aircraft that the engine is operating and to ensure nobody comes up too close to the running engine.

Some aircraft have boarding steps from the ground up, and these spirals also help warn passengers and crew that the engine could be working and not get too close.

In flight these spirals flicker as the engine rotates at high speed, scaring birds and allowing them to fly clear of the engine.