Two-Part Car Horns / Bicycle bells
Ever happened to you that you honked your car horn or rang your bicycle bell just to signal to someone else "hi, am here" but they misunderstood it as an aggressive gesture?
Why not allow all bells and horns in traffic to make two different sounds - one for "hi / hello / look here" and one for "danger / jump aside / buzz off"? The "danger" signal should be the one that comes naturally, e.g. when you press the car horn really hard. The lightweight friendly signal could sound when you push the horn only lightly (technology already exists in electronic drums!) or when you pull the bell trigger in the opposite direction.
Reward: Set of free bicycle bells