Back in July 2012, Google introduced a new feature for consumers to mute AdSense ads. In fact, that feature is still documented in the remove unwanted ads help page at Google.
But I believe that feature disappeared when Google introduced their new AdSense ad formats.
In fact, when I check my own AdSense ads, I see them on some sites but not most.
Here is an animated picture without the mute this ad feature:
Here is an animated picture with the mute this ad feature:
I know this is not new, but it doesn't consistently show more often than not.
Forum discussion at DigitalPoint Forums.