If you find a lost card, either turn it in to an employee of the business where you found it, return it to a branch of its affiliated bank or call the customer support number on the back of the card.
As much as we might like to think nothing bad will ever happen, that can be out of our control at times. Maybe you left your credit card at the bar, or perhaps you dropped it in the back of a cab.
If you find someone's credit card in a store or on a sidewalk, your first thought is probably to do the right thing by making sure it doesn't get into the wrong hands. But there is some risk involved ...