nabilg:
Thank you for your answer.I live in France, so both French and EU law apply. That's right, there is probably some legal ou insurance-related issues that I shoud consider. I was wondering if changing turn signals would be a problem, even if they are still compliants. Maybe I shoud take care of that.
Otherwise, do you think it is bad to power an arduino board on and off very often ?
I personally would not be turning the arduino board on and off like a turn signal.
i would have the Arduino turning a MOSFET on and off which is what controls the LED strips being used for turn signals.