Buoys are floating aids to navigation.
They may have the shape of a cone, can, pillar, spar or sphere, have numbers or letters or both.
They have a distinguishing color, and a top mark if any, and they also have a characteristic light.
They may be equipped with a distinctive sound signal, for example, a whistle, gong or bell.
A buoy is usually equipped with a radar reflector that enhances the echo on a radar screen.
It can also be equipped with something called a “RACON” that allows the buoy to emit an identifying specific and independent radar signal.