It's a very sticky situation, at least in the US. People can (and do) file frivolous lawsuits all the time, and your malpractice insurance doesn't really care if there's grounds for the suit, only that you have been sued. I'd be more worried about the rate increase due to a sue-happy patient than anything. My brother, who is a shock-trauma doctor, will only offer help to people outside of his hospital if they're not going to be OK till a first responder arrives. Example... we stopped when we saw the teenager fall out of a tree and land squarely on his head; the kid was knocked unconcious and my brother gave first aid till the paramedics we called arrived. But when he was at a gun show, and one of the other visitors accidentally shot himself in the hand with a gun he thought was not loaded, my brother didn't even identify himself as a doctor--- it was not a life-threatening wound and paramedics got there about 3 minutes after being called. He's very afraid of being sued, so if it is something that can wait a few minutes till a paramedic or EMT arrives, he lets it wait. I know that sounds horrible but having dated a DC cop for several years, I know all sorts of wacky stuff people sue for, and I wouldn't want to expose myself to that risk if it was "just a flesh wound."

Also if you are affiliated with a hospital, you should check with the legal or PR department for their policies. My brother has to carry two sets of business cards, one of which does NOT list his employer; he is not allowed to do anything that might drag the hospital into a lawsuit too. Some private practices have this sort of rule, too, so unless you're your own boss, let your employer guide you on this one.