I'm curious what law they would be upholding unless there was some legal restriction apply to the anchorage(that could happen). I don't doubt what you're saying at all, I just wonder about the real legalities. I think you're right that the Feds may not be protecting our anchoring rights, and local laws are bending the rules down that way.
Following another blog of someone in Georgia ICW right now, they too ran into some nasty signs no doubt to discourage derelict boats.
It's been a long time since we've been down that way. Back then, some areas of So. Fla. had NO ANCHORING signs and some heavy legal threats psoted. I never tested one of them but we spent some time anchored in West Palm Beach off Peanut Island, and that was a mess. We hauled our boat ahead of schedule(we shipped it back home) to move ashore as it was full of derelict boats and some sketchy folks that had NOTHING to do with boating! Those boats pretty much destroyed that beautiful anchorage and our ability to anchor for a week in that entire area.
The other thing I've found, especially here in Maine. When somebody anything similar to the "New York ex pat set" tries to bend any rules or laws in their favor(especially to enhance their view), they don't get very far(in fact around here, it usually backfires! ).
Maybe in Florida there's more incentive for the people working in local town government to bend for the folks from away? Could be due to high caliber realestate speculation.