Emergency obstetric care (EmOC) signal functions are a shortlist of key clinical interventions capable of averting deaths from the five main direct causes of maternal mortality; they have been used since 1997 as a part of an EmOC monitoring framework to track the availability of EmOC services in low- and middle-income settings. Their widespread use and proposed adaptation to include other types of care, such as care for newborns, is testimony to their legacy as part of the measurement architecture within reproductive health. Yet, much has changed in the landscape of maternal and newborn health (MNH) since the initial introduction of EmOC signal functions. As part of a project to revise the EmOC monitoring framework, we carried out a meta-narrative inspired review to reflect on how signal functions have been developed and conceptualised over the past two decades, and how different narratives, which have emerged alongside the evolving MNH landscape, have played a role in the conceptualisation of the signal function measurement. We identified three overarching narrative traditions: 1) clinical 2) health systems and 3) human rights, that dominated the discourse and critique around the use of signal functions. Through an iterative synthesis process including 19 final articles selected for the review, we explored patterns of conciliation and areas of contradiction between the three narrative traditions. We summarised five meta-themes around the use of signal functions: i) framing the boundaries; ii) moving beyond clinical capability; iii) capturing the woods versus the trees; iv) grouping signal functions and v) measurement challenges. We intend for this review to contribute to a better understanding of the discourses around signal functions, and to provide insight for the future roles of this monitoring approach for emergency obstetric and newborn care.