Factors affecting preference ratings of prohibitive symbols

A sign consisting of a pictorial overlaid with a red circle-slash (i.e., a red circle with a red slash) is used ubiquitously to convey the message that some activity is prohibited. The purpose of this study was to investigate the effects of pictorial solidity, size, and direction of elongation (DE) of the pictorial and orientation and thickness of the red circle-slash on the preference ratings for prohibitive symbols. Solid (filled) pictorials were rated better than pictorials in outline form. Pictorials with a size equal to or greater than 75% of the length of the inner diameter of the circle-slash were rated higher than pictorials 50% in size. The effect of pictorial DE was not significant: pictorials with a greater vertical DE (i.e., tall/thin pictorials) did not differ from pictorials with a greater horizontal DE (i.e., short/wide pictorials), in terms of their preference ratings. However, pictorial DE interacted with slash orientation. Diagonal slashes were rated better than vertical or horizontal ones. Further, symbols were rated better when the thickness of the red circle-slash was such that its resulting area comprised 25% of the total area inside its outer circle at least. Moreover, the interaction of pictorial size and slash thickness indicated that the preference for prohibitive symbols of thicker slash and smaller pictorial size might be degraded drastically. Implications of the results for the design of prohibitive symbols were discussed.