This buoy has a RACON attached. When your radar beam hits this buoy it sends back a strong signal that shows up as a prominent bright echo on your radar screen in the form of Morse code "N". These signals are excellent aids to navigation as they are unmistakable in ID. But if you have never seen one, you might be startled when they first appear. The inset (not presented here) shows how they appear on your radar.
RACON is something one could look up in another part of the program.