The phrase "official stamp" refers to an official mark or seal that is used to show the authority or approval of a particular organization or person on a document or item. Full definition
So there is our first official stamp on Arsenal's two new Gunners, and thankfully it is Lucas Perez who now has a couple of weeks to settle in before we can roll him out for his debut. (justarsenal.com)
Under the proposed agreement, in addition to getting NASA's official stamp of approval, the game could be sold in retail shops. (scientificamerican.com)
Their retail success led to Capcom's official stamp on the port of The Legend of Zelda: A Link to the Past and Four Swords to Game Boy Advance in 2002; and its direct involvement in the creation of the critically acclaimed The Legend of Zelda: The Minish Cap for Game Boy Advance in 2004. (gamesradar.com)