Years of scientific research has told us that humans reach well to anything that appears to have a face - and especially a smiling face. It's one of the reasons we're so fond of cats, even when cats often seem so indifferent about us! It's also the reason that the logo of thrift and donation store Goodwill is so ideally suited to its purpose.
Whenever we get involved with a charity - whether that's by donating to one or buying from one - we like to feel like we're going something good for the world around us. Goodwill helps to provide us with that feeling by featuring a logo that seems to smile at us. The effect is an optical illusion - it's just a close-up of part of the letter 'G,' but it reminds us to go into the store with a smile on our face, and a positive attitude.