See, once upon a time, many cars came with a back seat which could be removed to serve as a cushion for...well, anything you might care to do while on a long trip out into the country.  These two were concerned with something else (look at her expression)  and someone came along and stole the car.  (Peter Arno's version of this gag brought a LOT of complaint to The New Yorker when it appeared, and it became a standard in the postcard world until the joke just didn't work any ore.)  This is a Scottish postcard of mid-century origin, never mailed or messaged