A mod of the fantastic chrome-clacks - https://github.com/newfolder0/chrome-clacks by Peter Bell et al.
I really liked the idea of a Chrome extension to highlight pages including the "X-Clacks-Overhead" HTTP header. Unfortunately, I'm also really picky, and I like to tinker, so I couldn't leave the existing extension alone. This version shows an icon of Terry Pratchett when the site contains the header, but also logs the hostname to sync storage, so that when you click on the icon, it shows you all the places that you've seen it before.
For more info on the HTTP-based tribute to Sir Terry, see here: