What must you remember when you see this traffic sign?

Your choice (answer 1) is correct. This sign is a warning that the street lighting is switched off at night (or does not stay on all night). The idea is to make you aware that the road may become much darker later, so visibility and hazard recognition get worse.

What you should do in practice is adjust your driving for darkness: reduce speed if needed, keep a larger safety distance, and use your vehicle lights correctly (low beam/high beam when permitted, and don’t rely on street lamps being on). This sign does not mean you can park without lights, and it does not create a parking prohibition; it only informs you about missing night-time lighting.