I just looked at one and it does say "O-72 FULL CURVE" underneath. It's raised type molded as part of the plastic, along the inner part of the curve, near one end. The other end has a lot of the Lionel, Patent Pending, etc.. info .
Depending on who is looking it may be hard to see, but it is most likely there.
I am pretty sure all FT has similar markings underneath.
-Dave