Final answer:
The proper whistle signal to warn people standing near the edge of the platform is a loud and clear sound made by blowing air through a whistle.
Step-by-step explanation:
The proper whistle signal to warn people standing near the edge of the platform is a loud and clear sound made by blowing air through a whistle. This whistle signal is often used in situations where people need to be alerted or warned of an incoming train or any other potential danger. The whistle sound serves as a clear auditory signal that can grab the attention of individuals nearby and alert them to move away from the edge of the platform for their safety.