**Pedestrian-operated motor-cultivators** are not required to have acoustic signals. These vehicles are considered **special vehicles** and are not specifically mentioned in the regulations regarding the use of acoustic signals. Acoustic signals are mainly used to prevent accidents, overtake on roads outside urban areas, or in emergency situations, such as when performing a priority service. Pedestrian-operated motor-cultivators are not used in these situations, so they do not require acoustic signals.

On the other hand, **bicycles and motorcycles** must have acoustic signals, as they are vehicles that travel on roads and may encounter situations where it is necessary to warn other drivers. **Agricultural tractors**, although they are special vehicles, may also need acoustic signals in certain situations, such as on rural roads.

In summary, pedestrian-operated motor-cultivators are not designed for situations that require the use of acoustic signals, unlike bicycles, motorcycles, and agricultural tractors.