Have you ever thought about why qualities whose definitions are elusive, such as those of a sunset or a half-opened rose, affect us so powerfully? According to de Saussure (Course in general linguistics, 1983), the making of meanings is closely related to the production and interpretation of signs. All types of design, including advertising design, are about meaning-making. This study examines the effectiveness of a problem-based learning (PBL) approach in enhancing student designers' creative flexibility in advertising design. A semiotic approach is employed to examine hand-sketched print advertisements for a bakery promoting the metaphorical theme "Bread is Life" produced by participants in a series of PBL workshops (the experimental group) and a series of lecture-based workshops (the control group). The visual representations realised through these sketches in association with the metaphor were categorised into different signifiers by five experienced creative directors and are compared on an inter-group basis. The results of the semiotic analysis show the experimental group to have generated a wider variety of signifiers than the control group, thus reflecting the higher degree of creative flexibility that results from the use of a PBL approach. Theoretically, this empirical study addresses a number of conceptual issues in advertising design, creativity, problem solving, divergent thinking and semiotics. Practically, it contributes to an understanding of how a PBL approach can contribute to the enhancement of semiotic association skills amongst student designers in a professional communication context.