Copyleft symbol

Copyleft uses copyright law to keep a work free to share. Ordinary copyright says "all rights reserved": apart from narrow legal exceptions, nobody may copy or alter the work without permission. A copyleft licence grants that permission up front, with a catch. Anyone who passes the work on, changed or not, must do so under the same terms, so the freedom cannot be removed down the line. The best-known examples are the GNU General Public License (GPL), which covers the Linux kernel and a great deal of other free software, and the Creative Commons Attribution-ShareAlike (CC BY-SA) licences, which cover Wikipedia's text. Free here means freedom, not price; copyleft works can be sold.

The word is a pun on "copyright" that Richard Stallman made famous in the 1980s through his GNU Project, the project that launched the free-software movement. The symbol is the same pun in picture form: the C in © turned to face the other way, so the sign reads as "copyright, reversed". For years it lived as a drawn logo and in a few special fonts; it became a proper Unicode character only in 2018. Plenty of fonts still lack it, which is why you may see an empty box where someone meant 🄯, and why some people type the stand-in (ɔ) instead.

What does it mean when you see it on a work?

The author is signalling that copying and sharing are welcome. On a program, a book, a font or a website footer, 🄯 says "this is meant to be reused"; the licence named alongside (GPL, CC BY-SA and so on) explains how. It is often paired with a joke that flips the usual legal phrase: "All rights reversed" or "All wrongs reserved".

One thing it does not do is replace the copyright notice. Copyleft rests on copyright, so a proper notice still names the copyright holder, usually with the ordinary © sign, and then states the licence. The Free Software Foundation, which publishes the GPL, calls swapping © for a backwards C a legal mistake. Treat 🄯 as decoration that tells you the spirit; read the licence for the rules.