https://www.quora.com/What-is-google_vignette
Seems the sites in question are using Google Adsense auto ads. where the site itself is adding #google_vignette to the URL on the page.
There's a pic on this page that shows what it's supposed to look like. Of course, if you're using an adblocker, the ad will probably be missing where you just see a blurred page.