@rek @neauoire We were once saved from a possible wreck by recognising Uniform flashed at us by lamp.
Dark night, sailing on a reach, parallel to a steep-to lee shore, aiming to pass between a tug and the shore. Tug flashed 'U' at us. Turned out we were sailing into the bight between tug and it's unlit, aground, tow on the shore.
A hasty 180° performed!