An isolated danger mark differs from cardinals in as much as they are both indicating danger but different types. A cardinal mark indicates an area of danger whereas an isolated danger mark indicates a lone obstruction such as a rock.
In theory you can circle around an isolated danger mark. However, always check the chart and surrounding area before you try it.
The isolated danger mark is black and red horizontal stripes. (you may remember the Beano character Dennis the Menace).
It has two black balls as a top mark. If you hit it, it’s a balls up!
The light for this mark is a white flashing light. It will flash twice in every 10 second period. On a chart this would be denoted as 2 Fl 10s.