A paperclip standing for a file carried alongside a message.
A paperclip marks a file sent alongside a message, or the control that adds one. The metaphor is exact — something clipped to a document rather than written into it.
Marks a file carried alongside a message, and the control that attaches one.
Contexts: Software
A single line doubling back on itself twice to form a narrow elongated loop within a loop, set at a slight angle.
Both are used in software contexts.