What applies from this traffic sign onwards?

Your answer is fully correct. This sign marks the beginning of a built-up area (town or village boundary), which means specific rules apply from here onwards:

1. You may not sound your horn to signal your intention to overtake. In built-up areas, honking is generally prohibited except in emergencies to reduce noise pollution and improve safety.

2. Parking cars may be safely marked with parking lights. When parked on the roadside during darkness or poor visibility within towns, using parking lights is allowed to signal your vehicle's presence safely.

The third option about driving with parking lights in the darkness does not apply here. Within built-up areas, you must use full vehicle lighting (headlights) while driving in darkness for sufficient visibility and safety, not just parking lights.

Remembering that such signs indicate a built-up area will help you recall these traffic rules for future driving theory tests.