I thought about it for a minute, and sure, given a chrome.exe HWND, I can't think of a way to tell if it's Incognito.[1] But companies work with important vendors on major features all the time. If they think it's important enough to exclude private windows in Edge, they surely could have worked with Google to figure out something.

> nor should there be, obviously, as it would defeat the purpose

No it doesn't. Incognito mode is about leaving no trace on disk, that's all. Recall is the one defeating that purpose right now, if TFA is accurate.

[1] Not saying it's impossible. Only that I can't think of a straightforward solution in a pinch with my limited Windows experience and hacking skills.