This paper derives a key monotonicity property common to dividend signalling models: the greater the rate that dividend income is taxed relative to capital gains income, the greater the value of information revealed by a given dividend yield, and hence the greater the associated excess return. This monotonicity condition allows us to distinguish the hypothesis that dividends are used as a signalling device from the hypothesis that dividends contain information but are not used as Spencian signals. The monotonicity conditions are tested with robust non-parametric techniques. Although we find strong evidence that dividend announcements contain information, we find no evidence to support dividend signalling. The same results are inconsistent with tax-based CAPM arguments.