A generic, project-specific namespace ("p")?

Can we agree on a project-specific namespace?
This should not be used for frameworks, so it can be used in a project without hesitation.
So far I have always used "cd", (customer data) but maybe another one is more suitable.

    p- (project, private)
    x- (commonly used?)
    c- (customer)
    ps- (project specific)

"p" or "x" are my favoritex.

What is your opinion?