Your question prompted me to take another look at the safety code.
http://www.modelaircraft.org/PDF-files/105.pdf

I posted a question to the AMA. Essentially I asked what site rules means.

Some communities require permits to fly RC aircraft anywhere in thier jurisdiction. I live in Nassau County in NY. An RC permit is required. In order to get the RC permit you have to have a county leisure pass, which permits you to use the parks, and you must have a current AMA card.

Unless you checked, you probably would not realize you were in violation until you filed an insurance claim and were turned down. The code makes it your responsability to discover the site rules, as I read it.

So, even if a cop never stopped me, and even came over to watch, I presume if I was not in posession of a permit, I would be considered in violation of the safety code.

The fact that a cop never said anything is not a legal endorsemet of your activity, as I understand it.