My only source is my business partner, but it's a pretty good test. At 10-15 feet, you can only see features as geometric shapes, but on very well-designed sites you can probably tell what you're "supposed" to do. This is most effective for signup and purchase flows, where simplicity matters most, but I think it can lead to insights on pretty much anything.
1) "across the room" -- stand 10 feet away from your machine and see if you can tell what you're supposed to do
2) "don't make me think" -- i'm sure anyone who has ever used a website has to think about this one.
if you actually want people to sign up, make it easier, not harder. save your creativity for your content.