Am I liable for an auto accident if I'm a cosigner but not on the title, registration, or insurance policy?
It might be possible to sue you successfully if someone brought evidence that your brother was absolutely totally unsuitable to drive a car because of some character flaw, and without your financial help he wouldn't have been able to afford a car. So helping a brother to buy a car, if that brother is a drinking alcoholic, or has only a faked driver's license and you know it, that could get you into trouble.  A not unsimilar situation: A rental car company could probably be sued successfully if they rented a car to someone who they knew (or maybe should have known) was disqualified from driving and that person caused an accident.