People sometimes believe that they can plead ignorance if they violate a law or ordinance, meaning that they will not get in trouble for breaking the law because they didn't know about the law.  This is not true. 

Even if you did not know that what you did was illegal, you are still responsible for your actions.  All laws are written and recorded and are available to everyone.  It is possible for you to find out if something is illegal.  This encourages people to find out what is illegal and to follow the law.  If people were allowed to plead ignorance, the law would not be as effective as it is.