What type of messages may involve the use of written notes or letters?

Written messages are specifically designed to convey information through written language, making them a direct and clear means of communication. This category includes various forms, such as notes, letters, emails, and text messages, all of which rely on the written word to express thoughts, ideas, or information. The clarity and permanence of written messages allow them to be revisited and referenced later, adding to their effectiveness in communication.

In this context, while verbal messages involve spoken words and non-verbal messages encompass gestures, facial expressions, and body language, they do not include any form of writing. Interference refers to distractions or barriers that hinder effective communication, which does not relate to the medium of written communication. Therefore, written messages are the appropriate choice as they encompass the use of written notes or letters.