Test the symbols on your target audience. Or, rely upon the testing of others. The current test procedures for symbols have recently undergone a shift. Rather than insist that all symbols have a high comprehension rate, it is more important to find the best symbol for the sign. Symbols often need a reinforcing text message. Abstract symbols, such as the biohazard symbol or the radiation trifoil are examples of symbols that need an accompanying text message.

Abstract symbols are hard to understand and must be learned.