This chapter summarizes the results of studies investigating how to use pictograms to convey safety information in workplace, as well as some new insights into how to study the effects of iconic nature of pictogram information. First, it defines what a pictogram is and then describes empirical data reported in specialized domains publications, when assessing the role of pictograms in conveying recommended modes of behavior. The chapter discuses the theoretical contributions of semiotics, of cognitive psychology for pictogram readability and understanding, and of the contextual categorization approach, a theory that accounts for contextual effects involved in the understanding of pictograms. It describes the methodology, some examples and some outcomes from studies on creation of taxonomies and ontologies of pictograms for evaluation and design. Finally, it provides recommendations for ergonomic conception of pictograms, in order to improve the readability and understanding of pictograms used to convey user safety information in workplace. Keywords: contextual effects; design; ergonomic conception; ontologies; safety information; semiotics; taxonomies; understanding of pictograms