What is an essential requirement when using letters of transmittal?

When using letters of transmittal, it is essential to include a notice under banner markings. This practice serves to clearly identify the classified nature of the documents being transmitted, ensuring that recipients understand the sensitivity and handling guidelines associated with the information. Banner markings provide a visual cue that emphasizes the classification level, helping to prevent unauthorized access or mishandling of the materials. The presence of such notices aligns with best practices in information security, promoting awareness among all personnel involved in the transmission and handling of classified information.