Rather than throw my 2 cents into a rather long thread, that was already starting to go down some ratholes, I figured I'd share my thoughts on planning activations and what I have done, to make sure that my operations would go smoothly, follow the rules, and be fun all around.
Once I know the hours, I look at the type of park - if it is a park that is a large recreation area, where people would bring all kinds of equipment by the nature of what is in the park (camping, fishing, boating, photography, etc.) I just go, because I know my little activation with my small equipment won't really be any different than any of these other things going on. If I see (using Google maps) that the park has large parking areas where I could just operate from my car unnoticed, I pretty much do the same thing.
However, for parks that are small, if I know ahead of time when I'm going, I just e-mail the superintendent and ask. So far I've only been told no once - I passed that info along through the proper channels on the ARRL site, and I picked another place to go - that simple! If the park I'm near is a small one, and I have any doubt, I just don't activate!
Tonight was a good example though, of a case that wasn't clear. The hours on the park web site looked to me like they were hours for a visitor center, but looking on Google maps, I could see that there was a lot of ground, and even a trailhead parking lot away from the main buildings. I figured I'd stop and scope it out. There were no signs posted at the lot when I pulled up, but there was a sign, that had some map / flyer holders, so I grabbed one, and found what I was looking for: