赤信号

1. Origins, structure, and basic meaning

• Structure: 赤信号, read あかしんごう, means a red traffic signal and figuratively a warning sign of danger.
• Basic usage: It can require a vehicle to stop at an intersection or characterize lack of sleep as a warning of declining health.

2. Common pitfalls and similar expressions

• A traffic signal and a warning sign
  • It denotes a red traffic light requiring a stop and can metaphorically describe a warning sign of worsening health. The second use is not a physical signal lamp.