Do advertisers know which publishers have them blocked?

Via AdSense publisher's Competitive Ad Filter

[farmboy]

As an AdSense publisher, if I place a site in my competitive ad filter, does the site owner know I am blocking his ads from my site?

FarmBoy

[netmeg]

Nope.

If I was targeting you and my ads didn't show, I'd probably suspect. But there's no notification or anything that I'm aware of.

[eWhisper]

I don't think so either. The advertiser would just know that their ads were getting 0 impression on that placement.

It would look the same as when Google lets you choose a site for placement targeting where it's either not available, or is set to manual review (and might take a while for them to get reviewed).