Background: Although communication is a key component of US strategies to prevent suicide and there are a number of marketing campaigns promoting messages that suicide is a preventable public health problem, there has been little evaluation of these campaigns. Aims: The study describes the development of a checklist of best practices for suicide prevention communication campaigns and the use of the checklist to evaluate California's investment in "Know the Signs" (KTS-M), a suicide prevention mass media campaign. Method: We conducted a literature review and solicited expert feedback to identify best practices and then used the RAND/UCLA appropriateness method to assess whether KTS-M was consistent with the identified best practices. Results: Overall, experts agreed that KTS-M adhered to most of the 46 checklist items and suggested that the campaign was among the best suicide prevention media campaigns they had observed. Limitations: The checklist was developed through expert input and literature review and focuses only on media campaigns. Conclusion: Given the nascent state of the evidence about what makes an effective suicide prevention message and the growing number of campaigns, the checklist of best practices reflects one way of promoting quality in this evolving field. The consistency between the experts' comments and their ratings of KTS-M suggests that the checklist may provide important guidance to inform the development of future campaigns and the evaluation of ongoing campaigns.