Lateral marks

The big green thing and the big red thing are lateral marks.

One marks port (left), the other marks starboard (right). A vessel must keep port markers to the port side and starboard markers to the starboard side. Which one is which depends on which region you're in.

The International Association of Lighthouse Authorities (IALA) defines two regions: IALA A and IALA B. Region A includes Europe, Australia, New Zealand, most of Asia and parts of Africa. Region B includes the Americas and parts of Asia.

In region A, the red marker must be kept on the left when entering the harbour (from the sea) or a river, and vice versa in region B. They tend not to be on the road like this.