Final answer:
Notations like 'Enc.' or 'Att.' are commonly used to indicate attachments to a letter, and physical cues like staple marks or clip imprints might also show that something was attached.
Step-by-step explanation:
The notation used to indicate that something is stapled or clipped to a letter, particularly in the context of a business or formal communication, is often indicated by a special notation such as 'Enc.' for enclosure or 'Att.' for attachment.
Additionally, physical cues on the document, such as a staple mark, paper creases, or a clip imprint could suggest that an item was previously attached to the document. In literary texts, cues might be more descriptive, where a character may note the chafed edges or altered appearance of paper to deduce something has been attached or modified, much like in the provided literature examples.