Personally I don't see why you struggle with the point of these shaming memes on the basis you name. It's not about the dog (or the dice) being able to understand the message written on the sign: it's a joke, pure and simple, and DUH, obviously the animal (or object) being shamed isn't the target audience. It's just a form of socializing through commiseration: other dog owners/dice rollers will get the message, and be able to share their own stories, and a good laugh, and life goes on. What's the big mystery for you to get?