These photos were taken at the Griffith Park Zoo in Los Angeles in 1956. The humor, of course, comes from the clear irony of the sign: “NO DOGS OR PETS Allowed in Zoo.” Despite the explicit rule, Paul Newman is standing right next to the sign with a cat draped over his shoulder like a stole, calmly eating an ice cream.
The Siamese cat, named Louis XIV, actually belonged to the photographer, Sanford Roth, who took the pictures. Louis XIV was a bit of a celebrity in his own right and had also been photographed with James Dean the previous year.