Consumers cannot verify green attributes directly and must rely on such signals as eco-labels to authenticate claims. Using signaling theory, this study explored which aspects of eco-label design yield more positive effects. The study uses a 2 (argument specificity: specific versus general) x 2 (label source: government versus corporate) x 2 (product involvement: low versus high) experimental design (n = 233). Specific arguments consistently yield greater eco-label trust and positive attitudes toward the product and label source, but only with low-involvement products is source important, with corporate labels yielding more positive attitudes. Findings are discussed in terms of theoretical and managerial implications.