Which warning sign must be posted in all aquatic facilities?

In aquatic facilities, it is essential to communicate important information and ensure safety, which is why specific warning signs must be posted. "All of the above" is the correct answer as it encompasses multiple necessary signs that contribute to both operational clarity and safety.

Having a sign indicating "Hours of operation" helps patrons plan their visits appropriately and ensures that they are aware of when the facility is open, which is crucial for effective facility management.

A "Lost articles" sign informs visitors about the protocol for reporting and retrieving lost items, promoting responsibility and organization within the facility and ensuring patrons feel secure about their belongings.

Lastly, the "Running prohibited" sign emphasizes safety by instructing visitors to observe rules designed to prevent accidents, particularly in slippery areas around pools. These signs help create a safer environment and encourage adherence to facility policies.

Therefore, it is vital for aquatic facilities to post all these signs as they collectively promote safety, order, and efficient communication to the patrons using the facility.