At what exposure level must "Caution-Radiation Area" signs be posted in a radiography area?

The posting of "Caution-Radiation Area" signs is mandated by regulatory standards to ensure the safety of personnel in areas where radiation might be present. In this context, a sign must be posted when a radiation level exceeds 5 millirads (mr) in any one hour at 30 centimeters from the radiation source.

Choosing 5 mr as the correct answer aligns with the regulatory limit designed to protect workers and the public from unnecessary exposure. Signs serve as a critical warning, prompting individuals to take necessary precautions in areas where radiation levels could pose a risk. This helps to maintain awareness and promote safety measures within and around radiography workspaces. Other options provided do not fit the established threshold for requiring such signage, making them irrelevant for this specific question.