An isolated danger mark is placed on, or moored above, a danger that has navigable water all around it. It is black with one or more broad red horizontal bands, carries a topmark of two black balls, and shows a white Fl(2) light that separates it from the cardinal marks.
Two black balls: there is something right here to stay clear of. White Fl(2): two flashes, two balls.
Facts per the IALA Maritime Buoyage System (MBS ed. 2.0). The drawings are our own vectors. The light rhythm and colour in the drawing are illustrative: check the real characteristics of a specific buoy on the chart and in the list of lights.