A Guardian Bell is a small metal bell that attaches onto a motorcycle to ward off evil spirits. Guardian Bells have more of an effect when given as a gift.
"Legend has it that evil road spirits have been latching onto motorcycles for as long as bikes have been on the road. These spirits are responsible for mechanical problems and bad luck on a journey. Legend goes on to say that, by attaching a guardian bell to your bike, the evil spirits will become trapped inside the guardian bell. There, the constant ringing will drive them insane, making them lose their grip until they fall to the ground."