Hmmm. I wonder what you could leave in place of that stickie to see if he'd notice...
The same number on a different colored piece of paper...next with the sister's name written backwards, then mickey mouse's number, then a photo of mickey mouse's girlfriend waving at him, then a photo of minnie drinking a bud lite, then the number for AA, then a photo of someone's naked boobs...
You could make it into a kind of scientific study. See what - if anything - he finally notices.
Sorry if this comes off as insensitive to the A. But I sorely would like the rest of us to have some (innocent) fun, too.