Does the effective nuclear charge have a positive or a negative sign ? Or do I state the number as is ? ?

There is only one type of charged particle in a nucleus and that is a proton. So a nucleus cannot have a negative charge and you can state it as is, it is known to be positive.

No, effective nuclear charge does NOT have a positive or a negative sign.

By definition, the effective nuclear charge is the net positive charge experienced by an electron in a polyelectronic atom. It is understood that effective charge is "net positive charge", and thus it is needless to show the positive sign repeatedly.