I'm afraid I have no explanation for this other than what it appears to be: a lion with a turned up tongue which can only be for attaching a chain or something to. It's funny that I've never seen one like this before in Paris. It can't be unique but it's new to me. My only other theory would be that it's for holding a door knocker but it's not on the right place in the wall - i.e. a door - for that to be the case.