What does CSC mean

Only full members of the CSC are eligible to put the initials "csc" after their name. It is a recognition of a high level of achievement and years of experience in the film industry.

Here is a more detailed explanation from the "CSC News":

"The applicant must be professionally employed as a cinematographer for a period of at least ten years and must be fully qualified to assume the responsibilities as a Director of Photography, or must have to his or her credit exceptional achievement as a cinematographer."
Full Membership would therefore be reserved for those who had demonstrated their superior abilities, by submitting samples of their work to the membership committee for evaluation. It was clearly intended that anyone with Full Membership be someone who had demonstrated the skill required on feature or large commercial sets, with a full camera crew with an operator and assistants and a sizable lighting and grip crew. Such a person must have demonstrated this superior skill as a Director of Photography by technically achieving the artistic requirements of the Director, while at the same time managing a large crew.