Our usual everyday understanding is that the words “sign” and “symbol” are easily and often interchangeable. For example, if I ask: "Is a stop sign a sign?", most would answer yes. If I held it up and asked: "Is it a symbol?", most would say yes. A stop sign is a symbol used to remind someone of a law that says we must come to a complete stop at particular intersections. A stop sign is not the law. It causes nothing. It is the law givers and the drivers who do something- or not. The symbol of the Stop Sign doesn’t do anything on its own.
 
In our Church, signs and symbols have a different use and meaning.  We have seven particular signs called Sacraments. According to the CCC-

"The sacraments are efficacious signs of grace (efficacious- able to effect something; having the power to produce a result)…by which divine life is dispensed to us. The visible rites signify (are signs of) and make present the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions."                                                                                                                            ----      CCC,1131
So while the sign or symbol of the Stop Sign does nothing in its own right, Sacraments are signs that do something.