All signature restaurants are 2 dining plan credits, adult or child, lunch or dinner. The only exception is Le Cellier which is 2 credits for dinner only. The only available signature lunches are at CRT and Hollywood Brown Derby.
On the regular dining plan the allotments are the same whether you are paying one dining credit or two in most cases - entree, dessert and beverage for adults, no appetizer. Kids get appetizers but must select from the children's menu.
If you are on the Premium or Platinum Package Plans, all restaurants, including signatures, are one-credit restaurants.