The term "C" level executive just means they held a "chief" position.
Business definition: "C-level, also called the C-suite, is an adjective used to describe high-ranking executive titles within an organization. C, in this context, stands for chief."
In this case, Martin Schmieg was Chief Financial Officer to Cytometrics, Inc., Chief Financial Officer to Advanced Bionics Corporation, Chief Financial Officer to Sirna Therapeutics, Inc., Chief Financial Officer to Isolagen, Inc, and Chief Executive Office of Freedom-2, Inc.