Signalling nouns (SNs, hereinafter) as grammatical metaphors serve as effective clues to disciplinary epistemology. Based on self-built corpora, this study explores disciplinary variation in the use of SNs by investigating marketing and economics research articles (RAs, hereinafter). The results show that marketing RAs employ SNs with significantly higher frequency than economics RAs. In terms of grammatical patterns, marketing RAs prefer the “SN+ to-infinitive” pattern, whereas economics RAs tend to use the “SN+ that-clause” structure. Semantically, marketing researchers prefer modal fact and idea nouns to show a greater tendency for writer visibility, greater interest in factors influencing consumer purchasing behaviors, and the more empirical and experimental nature of marketing. In contrast, economics researchers prefer fact and idea nouns to explore the decision-making process of economic agents, and reveal the more hypothetical, econometrical, and abstract reasoning nature of this discipline. The choices of SNs reflect distinct disciplinary epistemologies between marketing and economics. This study sheds new light on the significance of SNs in revealing disciplinary variations, and creates a database of detailing the characteristics of SNs used in both disciplines, which can aid EFL learners and EAP practitioners to better use SNs to construct interpersonal relations with readers in academic writing.