I'm guessing the mascot changed to add or remove arms, and then they replaced only one of the bathroom signs later for some reason.
When bathroom signs have different pictures on the Mens vs. the Ladies, the pictures are expected to demonstrate some difference between the people expected to use the bathrooms.
In this case, it makes it appear that the establishment is saying that women have arms while men do not. This is counter to what a person might expect, and it is this subversion of expectations that some people might find humorous.
I see guys at the urinal with both hands on their hips and I wonder how they do that without peeing in their pants. I assume they must have huge hogs that reach the urinal and rest on the bottom. Mine is more like one of those wacky sprinklers where the spray hoses flail around everywhere when you turn on the water. I have to use my hand to control it, or it turns into a freaking Gallagher show, and nobody signed up for that.