Road Sign comprehension studies typically focus on differences among signs, demonstrating large variability in comprehension among different signs. Differences in features of sign design can be grouped into their shape, background color, and the symbol/icon in their center. This study demonstrated that specific sign messages can be presented with different sign features without detrimental effects on either comprehension level or response time. In particular, the choice of background color (yellow or white) appears to be inconsequential for comprehension. It seems that some sign characteristics are not critical to comprehension and consequently licensed drivers may even incorrectly identify a non-local sign as the standard sign that they actually encounter on the roads. However, other sign features - especially those relating to the icon/symbol - can be critical to comprehension when they violate the icon-concept compatibility, as it is represented in drivers' long-term memory.