**Acoustic signals** are sounds used to warn other drivers of the presence of a vehicle. These signals are important to **avoid possible accidents**. According to the information provided, their use is allowed on any type of road when it comes to preventing an accident. This means that, regardless of whether you are on a road inside or outside the city, you can use the horn to alert others and thus avoid dangerous situations.

Furthermore, the use of acoustic signals is an essential part of **preventive driving**, which involves anticipating the movements of other drivers and maintaining an adequate safety distance. These practices help reduce the risk of accidents and improve road safety.

Therefore, the correct answer is that acoustic signals can indeed be used to avoid a possible accident on any type of road.