Sounds like Philly is out of control.

Maybe you could just make arrangements to let them come in and salvage any of the historical items before you started the demo, and then they would agree to keep away once the wrecking began.

Might be a compromise to let them retain something of historical interest and value to them (assuming it had no salvage value to the demo contractor and you were going to trash it anyway) and to keep them from vandalizing your loaders and hoes.

Maybe that would be a win-win. Are they really interested in the historical preservation aspects or just trying to make trouble? If they are acting in the interests of historical preservation, it seems like they are going about it the wrong way, or maybe they are just frustrated that all the old buildings seem to get torn down in the end (they feel like the developers always win out).