In The Night of Miguelito's Revenge (S4 E12), at the beginnning of the episode as Jim West walks away from the newsstand vendor and closes the magazine, a 1967 ad for DieHard batteries ("The DieHard Fights the Common Cold", see http://bit.ly/13oN2xi) can clearly be seen on the right-hand page of the prop magazine, in a modern sans serif font.