Engine oil sign

Its either leaking it or burning it.

Any excess smoke from the exhaust?

When he tops up the oil, is he checking it has been fully topped up (using the dipstick)?

Different people have different definitions of what "topping up" means. By the time an oil level warning light comes on most cars need the best part of a litre of oil to get it back to the correct level. If he's just putting in a few cupfuls each time this could explain why the light keeps coming back on.

Also note that some cars will reset the oil level warning light if you open and close the bonnet regardless of whether you put any oil in. If you haven't put oil in, the light comes back on after the engine has been started, stopped and started again.

If he is genuinely putting in a litre of oil pretty much every time the car is run, there would be a lot of blue smoke coming out the back as it was burnt......

Can be warning lights for both level and pressure, it's often a faulty sensor issue

My Range Rover. L405 SDV8. Also, oddly enough, I've seen it on a Renault Trafic.

If it was a faulty sensor, the dipstick would show no loss of oil.

If your friend struggles to find the dipstick on his Range Rover, tell him it on range rovers is normally behind the steering wheel

What vehicle ? any history ?

And is this friend putting the oil where it is supposed to go ?

And as others have said, what exactly is this low oil sign ? and how do they then determine actual oil level before and after adding any if needed ?

Far too little information here.