MI state laws regarding no parking signs, contesting parking ticket

I was sitting out in front of my son's school waiting for him to come out for the day. There are dozens of other parents waiting as well. We are all sitting in our vehicles, with engines running-- I always believed that that is defined as "standing" not parking. There are signs posted all along the side of the street whic state "NO PARKING". A local police vehicle rolled slowly by and told the lot of us that we had to move on as there was no parking allowed. My first insticnt was to retort "I'm not parked, I'm standing", but I decidedthat would sound a bit lippy. I decided to find out what the actual definition of "no parking" was, but have had no luck finding anthing that defines the sign. Any information?