My favorite Signature is Flying Fish: cheese plate, tomato mozzarella salad, or mussels for an appetizer, scallops with risotto or char crusted steak for an entree, and whichever dessert trio they are serving that night. My steak at FF has always been better than any I've gotten at Jiko, California Grill, Citricos, Narcoosee, or even Yachtsman.
Favorites at the other Signatures include:
California Grill: sushi, flat breads, and cheese plate
Jiko: flat bread, lamb, maize crusted fish, and cheese plate
Citricos: gateau of crab
Narcoosee: almond crusted cheese cake
Yachtsman: lamb
Artist Point: mussels, portobello soup, and buffalo
Flying Fish is the only one where I really like all three courses though.