Semiotic labour signals and socio-technical stratification: a meta-synthesis of micro-credentials in digital credentialing ecosystems

Micro-credentials have emerged as modular, digitally mediated attestations of discrete competencies, signalling a shift in lifelong learning, workforce skilling, and digital credentialing. Following PRISMA 2020 guidance, this systematic literature review synthesised 86 studies from an initial corpus of 1,395 peer-reviewed and grey-literature sources published between 2015 and 2025. The review examined micro-credentialing ecosystems through three analytical lenses: employer signal efficacy, digital equity stratification, and platform infrastructurality. Findings reveal a complex employer epistemology. While some employers increasingly view micro-credentials as indicators of domain-specific expertise, adaptive learning dispositions, and job-ready competencies, scepticism persists regarding standardisation, verifiability, assessment rigour, and systemic legibility. From an equity perspective, micro-credentials offer flexible, asynchronous, and cost-attenuated pathways for non-traditional and marginalised learners, yet they may also reproduce exclusion through infrastructural deficits, device poverty, uneven digital literacies, and limited employer recognition. Technologically, the ecosystem is shaped by Open Badges, W3C Verifiable Credentials, blockchain affordances, and learner-controlled digital records, but remains constrained by fragmented quality assurance and weak portability protocols. The review calls for interoperability standards, equity-oriented design, transparent quality assurance, and context-sensitive empirical inquiry.