Innova discs have this
stamped on them, so I looked it up. And this is what they patent:

abstract

A one-piece flying disc formed of a flexible plastic with an annular rim and a central section joined together by an annular shoulder. The rim has a lower edge defining a lower plane of the disc and the central section has an upper zone defining an upper plane of the disc, with the rim having a triangular cross-section with a lower rounded corner forming the lower edge, an outer rounded corner, and an upper corner merging with the shoulder. The outer corner of the rim is located between the upper and lower planes, and the shoulder decreases in thickness from the rim to the central section.

claims

1. A circular flying disc comprising:

an annular rim and a central section joined together by an annular shoulder, and formed in a single piece of flexible plastic,

said rim having a lower edge defining a lower plane of said disc, and said central section having an upper zone defining an upper plane of said disc,

said rim having a substantially equilateral triangular cross-section with a lower rounded corner forming said lower edge, an outer rounded corner, and an upper corner merging with said shoulder, with said outer corner located between said upper and lower planes,

said shoulder decreasing in thickness from said rim to said central section, with the thickness of said shoulder at said rim in the order of twice the thickness of said central section, and with the outer surface of said disc from said rim outer corner to said central section having a continuous smooth curved lifting surface, and

the upper surface of said central section being substantially flat when the disc is stationery, with said central section being sufficiently thin and flexible to dome upwards when in flight.

What was interesting was that it was filed on October 27, 1983. Almost twenty four years ago! This thing should be expired by now (actually by 2000).