The difference between a CD and a Turbine CD, is that a Turbine CD not only holds the CD designation but also possesses a turbine waiver.

If you are applying for a fixed wing turbine waiver, you need two signatures, one from any waiver holder and the other from any Turbine CD.

There is also a small list of Designated Turbine CD's. See AMA pub 510k. The folks on this list are the only ones that can sign off on "rotary" turbine waivers.