Having eaten there proably 20 times over 4 years, I have to say that the menu changes with some frequency, and therefore I'd find it hard to name their Sig-dish.
If they offer a foie gras as a starter - I've always found it to be a winner. Thinking back, it seems to me that they have almost always offered a very nice braised veal chop which has been deboned and carved table side. That might be the most consistent item on their menu.
HTH