Same here, to be honest. I much rather search for the service's ANN thread to get more information about it. And there is usually a link to the official website there. Then I compare to see if it's the same that I found on search engines.
But the signatures have its use, otherwise the projects wouldn't be advertising here. You see them, the pictures and designs get stuck into your mind and you remember the names. Later down the road, if you need a service like the ones you saw advertised on Bitcointalk, those images come back. That's one way the projects benefit from signature campaigns.