You see a white marker with black vertical stripes. What should you do?
It simply means obstruction to navigation. Do not pass or avoid going there due to some obstruction. The marker indicates a problem or obstruction passing it so don’t pass between the markers and the shore.
A white buoy with black vertical stripes is a warning sign for a ship that an obstruction lays beyond the buoy. It means the ship should not pass between the obstruction marker and the shore.