Thanks for the chance to help. I am an attorney with over 12 years experience. Hopefully I can help you with your legal question.
First, lets talk about the trespassing charge
Here is the law in RI for criminal trespass
a) Every person who willfully trespasses or, having no legitimate purpose for his or her presence, remains upon the land of another or upon the premises or curtilage of the domicile
of any person legally entitled to the possession
of that domicile, after having been forbidden to do so by the owner of the land or the owner's duly authorized agent or a person legally entitled to the possession of the premises, shall be punished by a fine not exceeding one thousand dollars ($1,000), or imprisonment for a term not exceeding one year, or both.
This law is quite clear...the trespass must be "willful"...so the owner (or their agent) has to tell the person to leave and if the person does not leave? They are guilty of a crime.
What you describe is NOT trespass. It there was no indication that this was private property, and your son left immediately when he learned it was? He is not guilty of any crime
I would not pay the fine....since it is a criminal offense, if he pays the fine, he will have a conviction.
I would pay a lawyer to fight this.
Again, what you describe, this is not a crime...and the state has the burden to prove the crime, beyond a reasonable doubt. What you describe? No signs, no notice it was private property? Not a crime.
Now, lets address the issue of "reading of rights"
There is no legal requirement that a suspect be read their rights on arrest. This is a common misconception...but no place in the constitution
or any federal or state law is there such a requirement. Such a requirement would be unwieldy, since there is no basis for a requirement.
Now...there is a requirement under the 5th Amendment of the US Constitution that an individual not be forced to incriminate themselves. This led, many years ago, to the Supreme Court case of Miranda v Arizona, where the Supreme Court ruled that a criminal suspect, in custody of police, must be advised of their right to remain silent prior to interrogation.
This is the so called "Miranda" warning. And is administered by law enforcement (or should be administered by law enforcement) prior to any questioning.
In fact, if the police arrest a person, and interrogate him without first advising him of his right to remain silent, any statement given by the person can be suppressed (kept out of the criminal trial)
This is why all law enforcement agencies use the warnings...it allows them to interrogate the suspect and gain information to prosecute them.
IF they fail to issue the warning, they can not use the results of interrogation at trial.
But there is no requirement that they read the warning...and if they are not planning to question the suspect, they may decide not to issue the warning and legally it would not impact he police case at all.
So for your son, if he was arrested, and then interrogated and not advised of his right to remain silent, at his criminal trial, he could ask the judge to keep his statements out of the trial.