Not to be overly technical, but not necessarily. Why did the police respond? Was it a customer complaint or did the manager call? Who put the sign up? Was it from corporate (the business owner) or was it put up by a manager or other employee without authority of the business owner? If a business owner called the police, clearly the responding officers would have the apparent authority.And, if you think it has to be someone from the business, it doesn't
(b) For purposes of this section, a person receives notice if the owner of the
property or someone with apparent authority to act for the owner provides notice
to the person by oral or written communication;
The police DEFINITELY have that 'apparent' authority.
Having said that, I don't suggest "picking a fight" based on technicalities. If you innocently missed the sign that didn't meet the specs of the law, and the cops are there to arrest you for trespass, well, that is a whole other story.