Signs and boards warning seafarers for high-voltage overhead lines must have a self-reflecting surface.

The signs and boards are made of 2 mm sheet aluminium, edges bent, three sizes, high intensive reflecting foil. Symbols and text are black on white background.

Red border surrounds the edges, a red diagonal line on prohibitive signs. Recommended height from the ground to the lower side of the sign is 1200-1500 mm, making them clearly visible to seafarers.