Purpose – The purpose of this paper is to shed light on some important limitations of the ISO 26000 standard for corporate social responsibility (CSR) for the credible communication of corporate CSR claims. The paper aims to identify and explore firm-level strategies to signal adherence to the standard effectively and their legitimacy consequences for the standard. Design/methodology/approach – The identification of firm-level signaling strategies is mainly derived from an institutional description of the ISO 26000 standard and based on anecdotal evidence from current business practice, initiatives that have been taken worldwide by organizations such as national standards institutes, the ISO 26000 text and adjacent ISO documents, including ISO post-publication surveys. The paper is grounded in signaling theory. Findings – Five signaling strategies for firms are derived and explored which may reduce information asymmetries and engage in efficacious signaling of their underlying CSR quality and thus guide the communication of firms’ adherence to the ISO 26000 standard. Research limitations/implications – The findings urge to empirically investigate the use of ISO 26000 signaling strategies including their legitimacy consequences for firms. Practical implications – The findings of this paper have implications for decisions firms make when considering working with ISO 26000 and communicating their adherence, notably regarding the enhancement of the credibility of their CSR claims. Also, it offers suggestions for certification organizations, national standards bodies and policy makers that want to encourage the adoption of CSR standards, ISO 26000 in particular. Social implications – This paper may have implications for evaluating the CSR claims of firms by stakeholders and broader society. Originality/value – This paper is the first one to address inherent signaling problems of ISO 26000 and to identify signaling strategies to counter these problems in a structured way.