It would make the web completely unusable if every site you visited dropped a turd on your screen, even if it were a well-meaning turd. You would have to waste time working out how to get rid of it, then spend more time getting rid of each one as and when it appeared. Whoever thought of that as a design for their website needs their internet access revoked.
But if you want your visitors to have an easy way to remember where your site is, just indicate how to bookmark the site, and offer to send emails with site updates and stuff like that (for example on this site you can subscribe to forums and threads and an email can be sent whenever there's an update). Make sure it's friendly and that opt-in and opt-out are both simple to use and work. It does mean you're not in people's faces demanding they visit your site, but again I would have to question who on earth thinks that's a way to do business.