The Biker's bell.

Wiki:

"The Biker's bell - also guardian bell or ride bell - is an urban legend among some motorcycle enthusiasts. Like many pieces of folklore, it has several variations with elements common across all versions. Essentially, a small bell is hung from either the handlebar or the front wheel and serves as a device of mystic protection.

There are many websites that describe the legend of the biker's bell. Some of the pages are of private enthusiasts, others are of online community representatives, and yet other web sites containing the legend are of retailers of motorcycle equipment and accessories. There are even companies that specialize in selling these curious artifacts

A story of the biker's bell begins by describing evil road spirits that haunt motorcycles, causing mechanical failures. The bell serves as a trap, forcing these spirits into the hollow of the bell, where the constant tinkling drives them mad. Insane, the spirit falls to the ground, causing a pothole where it lands. While a powerful protective fetish in its own right, the bell's potency is doubled when given to the rider by a friend or loved one."