"Signature" isn't really just a dining plan term meaning the restaurant costs 2 credits. It means it's an upscale restaurant with upscale food offerings. Signature restaurant on the dining plan means something other than signature restaurant in general.
CRT isn't "signature" because of the food - it's in the 2 credit category because Disney knows guests will pay for the one-two whammy of princesses AND the castle.
When they first started the dining plan, CRT was one credit. That didn't last long. Just because it doesn't say "signature" on the Disney website doesn't mean it doesn't cost two credits. CRT is the only 2 credit restaurant that is not upscale in food terms, because the draw there is not the food. If you're looking for gourmet food, it's not the place. Yes, they still have the photo package included.