Works for me in Chrome. I assume it's cookie based, so it should work? I noticed that Chrome incognito keeps cookies until all incognito tabs are closed, so maybe close them, open a new incognito session and then reopen the page.
I've sent some Economist's articles to friends before and it detected Chrome's incognito both on Mac and Windows despite no other opened incognito tabs. Not sure how they do it but I assumed that Chrome has a "leaky" private mode.
