This 1967 Spanish commemorative stamp celebrates Día Mundial del Sello (World Stamp Day) and features a beautifully rendered reproduction of the classic 1850 6 Reales Certificado issue showing Queen Isabella II in profile. The central design is printed in deep blue with a bold red “R.” registration overprint, symbolizing certified and registered mail history. Issued by the F.N.M.T., it honors Spain’s early philatelic heritage and remains a popular collectible for thematic collectors of classics-on-modern, postal history, and Spanish commemoratives. A crisp, well-centered example adds strong display value to any Spain collection.