What signal indicates that oxygen is no longer required after an emergency?

The signal that indicates oxygen is no longer required after an emergency is "You may now remove your masks." This phrase clearly communicates to flight attendants and passengers that the situation has stabilized and that supplemental oxygen is no longer necessary. It serves as a direct instruction to remove the oxygen masks, ensuring that everyone can breathe normally without the need for the masks that may have been used during a period of cabin decompression or other emergencies.

Using this clear language is essential in emergency protocols to avoid confusion. In contrast, other options would not provide the same level of clarity or could imply that masks are still needed, which would not alleviate the situation for passengers and crew. Thus, this phrase is crucial for ensuring an effective and safe transition back to normalcy after the emergency has passed.