The number 555 is commonly used in North America as a prefix for fictitious phone numbers in movies and television shows. This practice helps prevent real phone numbers from being used and receiving unwanted calls. The 555 prefix is recognized by audiences as a signal that the number is not real. In the context of emergencies, dialing 911 is the standard procedure in the United States and Canada for urgent assistance from police, fire, or medical services. The 911 system is designed to connect callers quickly to emergency responders, ensuring timely help in critical situations.