What is a requirement of every commercial operator on duty and in charge of a transmitting system?

The requirement that the original license or a photocopy must be posted or in the operator's personal possession and available for inspection is crucial for ensuring that all operators in charge of a transmitting system are fully authorized to operate that equipment. This stipulation helps maintain regulatory compliance and accountability within commercial broadcasting and communication environments.

Having the license readily available means that, in case of an inspection by FCC representatives or other regulatory authorities, the operator can promptly provide proof of their qualifications. This not only supports adherence to Federal Communications Commission regulations but also contributes to operational integrity and safety in broadcasting operations.

The other options, while related to maintaining proper documentation and certification, do not fulfill the same immediate requirement for visibility and availability of the operator's authorization to control the transmission system. Therefore, the focus on having the license available for inspection distinguishes the correct answer as essential in promoting transparent and responsible broadcasting practices.