I have always found a triangle, you shouldn't assume the hi-viz vest will be provided (whatever the law or terms and conditions say). I guess you could always go back to the desk and ask for a hi-viz vest but in my experience it's often missing. This has been my observation both for long-term rentals from big brands (e.g. Avis) and for short-term free-floating vehicles in Paris.

I have always found a triangle, you shouldn't assume the hi-viz vest will be present in the car (whatever the law or terms and conditions say). I guess you could always go back to the desk and ask for a hi-viz vest but in my experience it's often missing. This has been my observation both for long-term rentals from big brands (e.g. Avis) and for short-term free-floating vehicles in Paris.