If there were no scars or external power source, could someone tell if I had an artificial heart?

Probably. Many artificial heart options have a sound that can be noted by being close to the person. It also depends on the patients weight.
Science fiction. Right now, there are no artificial hearts without scars/incisions to place them. Let's say someone invented a way to place a current artificial heart with internal power pack, we'd still be able to tell because it is a pump with no beat like a real heart. Of course if they were able to do that, maybe they would have invented a heart that beats but we have real medical questions to answer!