At one of my workplaces, they put an announcement on the door of the men’s and women’s bathrooms. I never read it. Why? Because every time I saw it, I was on my way to the bathroom. To read the sign, I would have had to stop on my way to the bathroom. Normally, I spend about 0 seconds standing at the entrance of the bathroom, 30 seconds staring at the blank tiles above the urinal or a few minutes staring at the inside of a bathroom stall, and about 30 seconds looking at the mirror above the sink where I wash my hands.
Given my natural tendencies, they should have put the important sign on the bathroom mirror, or inside the stalls, or above the urinals.
What’s a web equivalent? Maybe not putting ads on your registration page, because presumably you want your visitors to register more than you want them to click on an ad from a third-party site. Offer your visitors the right things at the right time and you will be more successful. Offer the right things at the wrong time and they might just walk right past you.