The Addressed To The Subject symbol (℁). Copy and paste it, or use its Unicode, HTML, and CSS codes.
More from Letterlike Symbols.
The quickest way is to copy ℁ from this page and paste it anywhere. You can also insert it with its Unicode, HTML, or alt code listed above.
℁ is U+2101 (decimal 8449).
Use ℁ in HTML to render ℁ on a web page.
On Windows you can type it with Alt+8449 (hold Alt and enter the number on the numeric keypad).
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