There are many types of symbols. Money from investors, banks or financial organisations is one such kind of symbols. The symbol system must map out reality in an isomorphic manner. We must be able to identify reality the minute we see the symbols arranged. The fifth requirement is universality.
Symbol systems are species of languages.
The language should be understood by all - in an unambiguous manner. A common terminology, a dictionary, should be available to both manipulator and manipulated. It cannot exclude certain symbols arbitrarily. It cannot ignore the existence of competing meanings, double entendres, ambiguities. It must engulf all possible interpretations and absolutely ALL the symbols available to the system.