In which case is this sign installed?
A caution sign only warns of the situation ahead so drivers can prepare; it does not replace signals or traffic control (Enforcement Rule, Appendix 6). Think about what the traffic light in the picture is meant to announce in advance, and remember that railroad crossings and school zones have signs with their own pictures.
Answer: ④
Explanation
This sign with a picture of a traffic light is a caution sign warning that there is a traffic light ahead (Enforcement Rule, Appendix 6, No. 125). When a bend or other obstruction blocks the view and the light's location must be announced in advance, it is placed on the right side of the road 50-200 meters before the light. The sign does not replace the signal, so you must follow the actual traffic light.
Legal basis: 도로교통법 시행규칙 별표6 125 신호기표지