I realise this is an old thread, but after a year, google has started a new campaign to try and dissuade users here from blocking ads by sending the message in the image below:
View attachment 24938
There's nobody logged into google on this machine, and the window can be closed by clicking on the cross in the top right hand corner (partly obscured).
Google is asking the user to allow ads, or try "YouTube Premium".
Interestingly, the adblocker on this machine, Ghostery, has detected that google is trying to have ads blocked, and has popped up a window of its own on the top right of the image, with the suggestion to open the video in a private window.
Fortunately, it wasn't necessary to use a private window since clicking both pop up windows off was sufficient to play the video.
The only hindrance was that the user was delayed by about 5 seconds before the video would run, but when it ran, it did so normally.
These windows have been fairly regular over the last few days, but decreasing today to a single occurrence.
It was surprising to get this message after about a year of not getting any, but I guess it's a neverending struggle for both the company and the ad blocking coders.