What symbol is used in Gmail to indicate an email attachment?

In Gmail, the paper clip symbol is universally recognized as the indicator for an email attachment. This widely accepted icon effectively communicates to users that there are files attached to the email they are viewing. The use of the paper clip symbol is intuitive, as it is commonly associated with holding documents together, thereby reinforcing the idea of files being included as part of the message.

In contrast, the other symbols listed do not specifically convey the idea of an attachment. An envelope typically represents an email itself, a pin could suggest that an email is important or flagged, and an asterisk is often used for denoting essential information or notes but does not imply associations with attachments. Thus, the paper clip serves as a clear and efficient visual cue for users to quickly identify attached files in their emails.