On my website, there is a top-menu feature that I would like that a new visitor sees and understands immediately. Maybe only 10% of the visitors will use it (that's why it doesn't deserve a bigger space than top menu), but I want to be sure that these 10% understand this feature immediately.
I'm looking for ideas about :
how to emphasize the presence of this option
how to prevent recurrent visitors to be annoyed by this message (maybe using cookies to detect if new/recurrent visitor?)
(Poor quality) example :
Note: this is not a meta question, I just used the site ux.SE as an example.