According to legend, harmful spirits lurk in the roadways and are always on the lookout for bikes to cling onto and cause mischief.  These invisible beings are called "gremlins", which means "to vex" in Old English.  They latch themselves onto motorcycles causing mechanical misfortunes and bad luck.

The myth goes on to say that to ward off these evil, malicious spirits, one has to affix a motorcycle bell onto the bike, ideally at the lowest part of the frame to trap the gremlins inside and drive them insane with the constant ringing of the bell.  This will make them lose their grip and eventually cause them to fall off.  (Have you ever wondered where potholes come from?)

Legend also has it that the power of the gremlin bell doubles when it is gifted to the rider and that it should be kept by the intended recipient.  This is so because the key to the bell's power is good will, and the spiritual power of the bell is "activated" when someone who cares about them gives it as a gift.  So share the good luck to all your riding friends. 

Guardian Bell & Legend