I was riding in Frick Park on South Clayton today and passed a woman walking on the trail. She seemed friendly enough, but just as I had passed her, she said, kind of under her breath, "you're not allowed to ride bikes here" or something to that effect. I turned around and came up along side her and asked her how she knew this, and we actually had a pleasant conversation. I told her why I thought it's ok to ride in the park, and she told me why she thought it wasn't, but it wasn't like an argument - we parted in a friendly way, acknowledging that we were definitely getting information from a variety of sources.
In the process though, she directed my attention to the following sign:

(text: Mountain bikes are not permitted in Frick Woods Nature Reserve / city code 473.03 bicycles confined to roads / no person in a park shall ride a bicycle on other than a paved, vehicular road.)
At first I thought that maybe the nature reserve was just a small part of the park, the areas where they're cultivating specific plantlife or things like that. but I went to http://www.pittsburghparks.org/park-featuresn and read "The 151 acres that Henry Clay Frick bequeathed to the City in his will were rededicated as the Frick Woods Nature Reserve on Earth Day 1991." under "natural areas". Thus, they seem to be saying it's not okay to ride any of the trails in all of Frick Park.
So this is really depressing. (I'm not suggesting, btw, that no one should ride in the park if it's against the law. I do, however, like to know when I'm doing something illegal. I didn't know about this.)
Anyway, I'd like to know if anyone knows anything about this - are we (frick mountain bikers) basically all criminals? Or is it some weird law on the books that there's an understanding isn't actually enforced? Or is there any sort of discussion going on about changing it?
The thing that makes me really confused (or maybe hopeful) is the sign above the first one.

It refers to the red area on the map, one of those places where they seem to be giving the plantlife special protection and they say "protected area. no dogs or skateboards. walk bikes."
So if you're supposed to walk your bike in the protected area, that seems to suggest that you can ride it in the rest of the park.
But the mean sign seems to suggest otherwise.
So what's the law? Are we really restricted to the pavement? Doubletrack but no singletrack? Excuse me while I go hyperventilate somewhere.
Input please. (Just looking for actual information, as opposed to advice on how to deal with my newly discovered low-life status. Thanks:0)
((Just kidding. I've always known I was a lowlife.))
I'm crossposting this on the PORC forum - more mountain bikers there (I assume) but the traffic seems really low.