This is a bike bell. It is intended to warn people you are approaching. I personally like the 8 ball design but it's not a fashion statement. It's a tool.
I ride a lot of multi use trails in parks all around southern California. People stand in the path, talk on the cell phone, listen to headphones full blast, let their dogs off leash, let the kids poke rattle snakes with sticks...
Yeah, a bell is a good idea to let people know you're coming. DING DING!
Without one, you are not heard until you are right up beside them and then they think you are the offending party. A bell can be heard from a longer distance. It gives people a chance to react. Great for blind curves.