Mermaid Restroom Sign
Actually, it could also be a merman, not just a mermaid. And the other sign -- is that, like, a pirate with a peg leg?
http://allmermaids.tumblr.com/post/6120342607/mermaid-toilet -via How Now, Spirit! Wither Wander You? | Image: unknown
I think pirates just go off the side of the boat, which is pretty much the same place a mermaid goes.