English: Wikipedia w:Merchant's mark: One such symbol combined the mystical "Sign of Four" with the merchant's name or initials. The "Sign of Four"[8] was an outgrowth of an ancient symbol adopted by the Romans and by Christianity, Chi Rho (XP), standing for the first two letters of Christus in Greek letters; this was simplified to a reversed "4" in Medieval times. The evolution of this symbol is shown in M. J. Shah's article.[9] The "Sign of Four" is called the "Staff of Mercury" (Caduceus) in German and Scandinavian literature on house marks