sissy bar

A sissy bar, also called a "bitch bar" or "passenger backrest", is an addition to the rear of a motorcycle or child's bicycle seat that allows the rider or passenger to recline against it while riding. Alternately it can serve as an anchor point or support for cycling supplies that are not part of the bike, including spare helmets, backpacks, or sleeping bags. Sissy bars are usually affixed to the rear fender struts, and are typically made of chrome-plated steel with a foam padded seatback for comfort. Some elaborate custom examples can extend three feet or more and often serve as mounts for novelty flags. (def. from Wikipedia)