"Good question. I think it’s fair do’s (is it Yorkshire dialect?). I don’t know why it would have an apostrophe except for show. “Fair dues” looks like an attempt at imposing faux-respectabilty. Anyway, doesn’t sound like much of a congratulation any way it’s written! How about “bravo!” which is what my two-year-old daughter says when she’s evacuated her bowels?" - Dave Nolan