Chart No. 1 · S 3.1
Racon (radar transponder beacon)
Buoys & beacons
A magenta circle and 'Racon' label mean the mark answers your radar with a Morse signal.
What it means
A magenta circle around a mark with the legend 'Racon' (plus a Morse letter, e.g. 'Racon (K)') means it carries a radar transponder: triggered by your radar, it paints that Morse letter as a line on your screen radiating from the mark.
Why it matters
Racons make key marks unmistakable on radar in fog or at night — the flash of Morse on the screen begins at (or just beyond) the mark's position. Magenta again signals an electronic/lit aid.