Have a 3D blu-ray question?

I just bought a 3D tv. I went to Hastings to rent a 3D blu-ray, but the movies I expected to be in 3D didn't list this feature on the box. e.g. Tron: legacy and Megamind were shot in 3D and I know they are avaialable in 3D blu-ray. Should it say on the box? Thanks for your input.