The validity of some theoretically-derived vocational diagnostic signs was examined to learn if a person's self-knowledge, occupational knowledge, and decision-making ability were predictable. Diverse samples of high school juniors (N = 1005), college juniors (N = 692), and employed adults (N = 140) were administered the Self-Directed Search (the source of the diagnostic signs) and the criteria for validating the signs (The Career Maturity Inventory, a decision-making task, questionnaire items about vocational choice, scales measuring identity, anomy, originality, and interpersonal competency). The signs for good decision-making ability (consistency and differentiation of the SDS profiles) predicted scores on the decision-making task more efficiently than any non-SDS variables. In contrast, the signs concerned with self and occupational knowledge had no convergent or discriminant validity. The results for the decision-making signs, however, imply some immediate practical applications and some potentially valuable theoretical investigations. (Data tables and a 21-item bibliography are included in the report.) (Author/AG)