Does Copilot watermark its text?
No published watermark. But its output does carry a character almost nothing else cleans: the non-breaking hyphen.
Microsoft publishes no text watermarking scheme for Copilot, and since it runs on OpenAI models, OpenAI's decision not to ship one applies. What we did find is more specific and more useful. Running a code-point census over a Copilot reply turned up five instances of U+2011, the non-breaking hyphen, in ordinary compounds: third-party, multi-touch, macOS-specific. It is visually identical to the hyphen you type. This is corroborated by reports that Copilot's Copy message button emits en dashes, em dashes, curly quotes and no-break characters in their full Unicode forms.
What Clipboard Sanitizer can do about it
Everything here is a character, so all of it. U+2011 was not in our rules until this analysis found it; it is now, and the macOS app straightens the whole dash family. The sample that prompted the change is in our corpus and you can check it yourself.
Questions
Why does the non-breaking hyphen matter more than it sounds?
Because you cannot see it and most cleaners do not know about it. It breaks searches for hyphenated terms, part numbers, and URL slugs generated from headings, and a diff will show a line as changed when it reads identically.
How did you find it?
By running the census over real Copilot output rather than assuming. It survived a paste path that had already flattened em dashes, precisely because nothing on that path handled it.