What does a large letter "X" placed near the runway threshold indicate?

A large letter "X" placed near the runway threshold is a universal visual indicator used in aviation to signify that the runway is closed. It serves as a clear warning to pilots that the runway is not safe for landing or takeoff operations. This marking is crucial for ensuring safety, as it alerts pilots to look for alternative runways or landing location. The presence of the "X" indicates that the runway has been rendered unusable or unsafe, perhaps due to maintenance work, obstructions, or other hazards. Consequently, pilots are trained to recognize this symbol and understand the implications, reinforcing the importance of situational awareness in aviation operations.