信号

1. Origins, structure, and basic meaning

• Structure: 信号 (しんごう) is a signal conveying information and can also refer to a traffic light.
• Basic usage: At a crossing, pedestrians wait for the green indication; a ship sends light toward shore as communication.

2. Common pitfalls and similar expressions

• Traffic-control device and optical signal from a vessel
  • 信号が青になる describes a traffic-light indication changing, whereas 光の信号 is a means of communication. The latter is not roadside equipment.