A conventional sign denotes a word or symbol that achieves a function through a linguistic property. For example, the letter "A" in English is a symbol that produces certain sounds when native English speakers translate a written word to speech.
A conventional sign needs no interpretation between a sender and receiver. The meaning of a conventional sign is generally understood as universal among people who speak the same language.
Another example is a yellow diamond sign along a highway or road in America that has a deer on it. This conventional sign warns motorists of a possible deer crossing. A large, red cross symbol is a conventional sign of first aid, the Red Cross organization or medical help.